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TRANSCRIPT
HALOGENATED 2-OXETANONES
APPROVED:
Graduate Committee:
tiJ. Major Profe
f " Committee Member
Committee pember
^Cdmmittee Member
m
Director of the Department of Chemistry
Dean' of the Graduate School
latel, Arvind D. , Halogenated 2-0xetanones. Doctor of
Philosophy (Chemistry), May, 1973, 68 pp., 4 tables,
bibliography, 44 titles.
The purpose of this investigation is threefold:
(1) to examine in detail the cycloaddition of halogenated
ketenes and carbonyl compounds, (2) to study the decarboxy-
lation of the resulting halogenated 2-oxetanones,and (3) to
investigate the effect of halogens in the halogenated
2-oxetanones on the nucleophilic addition reaction.
The generation of dichloroketene by the zinc dehalo-
genation of trichloroacetyl chloride in the presence of
simple ketones resulted in the formation of the corres-
ponding 2-oxetanones. Efforts to cycloadd dichloroketene
to -unsaturated carbonyl compounds were unsuccessful;
however, the zinc dehalogenation of trichloroacetyl chloride
in the presence of cyclic ketones resulted in the formation
of the corresponding 3,3-dichloro-spiro-2-oxetanones. These
cycloadditions ultimately lead to an important method for
the synthesis of methylenecycloalkanes.
Alkylhaloketenes also undergo in situ cycloadditions,
but only with activated carbonyl compounds. Cycloadditions
of alkylhaloketenes with aldehydes'produced both cis and
trans isomers in approximately equal amounts.
Any electronegative substituent on the 2-oxetanone ring
decreased the rate of decarboxylation. The presence of a
trichloromethyl substituent on the 4 position of the
2-oxetanone ring severely Inhibited decarboxylation. This
is perhaps an indication of the mechanism of the elimination
reaction, and suggests some charge separation whereby the
4 carbon assumes some positive character. Decarboxylation
of the alkylchloroketene-chloral adducts over an electrically
heated wire provided a useful synthesis for the exotic
trichloromethylallenes.
Electronegative substituents on the 2-oxetanone ring
increased the reactivity of the 2-oxetanone towards the
nucleophilic addition, and only acyl-oxygen bond cleavage
occurred during the nucleophilic addition reaction.
HALOGENATED 2-OXETANONES
DISSERTATION
Presented to the Graduate Council of the
North Texas State University in Partial
Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
By
Arvind D. Patel, B. S., M. S.
Denton, Texas
May, 1973
TABLE OP CONTENTS
Page
LIST OF TABLES iv
Chapter
I. INTRODUCTION 1
II. EXPERIMENTAL 16
III. RESULTS AND DISCUSSION 45
BIBLIOGRAPHY 66
iii
LIST OF TABLES
Table Page
I. 2-Oxetanonea from Dichloroketene-Ketone
Cycloaddi tions 44
II. 2-0xetanones from Methylhaloketene-Carbonyl
Compound Cycloadditions 49
III. Effect of Chloro Substituent in 3 Position
on Rate of Decarboxylation 55
IV. Effect of Chloromethyl Substituent in 4
Position on Rate of Decarboxylation... 56
iv
CHAPTER I
INTRODUCTION
The cycloaddition of ketenes and carbonyl compounds
yields 2-oxetanones (^-lactones).
C =C= 0 C = 0
;Staudinger first reported the cycloaddition of a ketene
to a carbonyl compound in 1908 (19). Most of the early work
was with diphenylketene and act -unsaturated carbonyl com-
pounds (20)^ such as dibenzalacetone, quinone and benzophenone.
The cycloadditions required temperatures of 130 to 140°C, and
at such temperatures the 2-oxetanones decarboxylated. Benzo-
phenone and diphenylketene undergo cycloaddition, to presumably
produce the corresponding 2-oxetanone, which decarboxylates
under the reaction conditions to yield tetraphenylethylene,
which is the only isolated product.
P h N Ph^ ^ C = C = 0 + > = 0
Ph Ph
Ph ^Ph
* c°2 Ph Ph
Since the elevated temperatures, required for cyclo-
additions are sufficient to cause the dimerization and poly-
merization of lower molecular weight aldoketenes and keto-
ketenes (21), most of the early work was limited to diphenyl-
ketene.
Kung (13), Zaugg (23), Hagemeyer (11)?and Quadbeck (18)
reported that in the presence of a suitable catalyst, carbonyl
compounds will undergo cycloaddition with ketene, to yield
isolable 2-oxetanones. Ketene was found to undergo cycloaddition
with aldehydes smoothly in the presence of mild Friedel-Crafts
type catalysts, such as zinc chloride, but ketones required
stronger catalysts, such as boron trifluoride etherate.
H s c = c = 0 + R > = 0 C a t a l r s t > H" R
Aldehydes were also found to react with ketoketenes in
the presence of suitable catalysts, resulting in the formation
of the corresponding 2-oxetanones (12).
K R „ . , . J > C = C = 0 + c = 0 Catalyst ?
H R
Oshe and coworkers have reported (17) the cycloadditlon
of ketene with chloral and hexachloroacetone in the absence
of a catalyst at 80°C.
H,
H
CC1, ,C = C = 0 :c = 0
H'
. 80° C
CCI3
It has "been recently reported by Bormann and Wegler (2, 3)
that the cycloaddition of ketenes to carbonyl compounds, to
produce 2-oxetanones occurs readily when the carbonyl function
is activated by electronegative substituents on the «<-carbon.
Thus the cycloaddition of several ketenes with activated car-
bonyl compounds, such as chloral, bromal, hexachloroacetone
and 1,1,3-trlchloro-1,3,3-trifluoroacetone have been
accomplished. The ketenes were generated in situ by the
triethylamine dehydrohalogenation of the appropriately sub-
stituted acyl chlorides.
R
R'
R .C AT C = 0
O it H
R - C - R ' " & + HN(Et).
I CI
More recently Bormann and Wegler (4) have reported that
dichloroketene undergoes cycloaddition with simple aldehydes,
to produce the corresponding 2-oxetanonee.
CI
CI CH -§-01
CI
Lei
v, • C= C = 0
9 R-C-H
CI
CI
o II
H
Dichloroketene was also found to cycloadd with °C-keto-
esters under similar conditions, to produce the corresponding
2-oxetanones; however, simple ketones such as acetone, cyclo-
hexanone and acetophenone did not react with dichloroketene.
C1 N O O O u
CI • CH-0-C1 + R-6-C-0Et
N( E t^3
CI
Clw
+ «N(Et), H >
EtO-C.
Recently Brady and Smith (5) have reported on the
stereochemistry of the cycloaddition of some aldoketenes with
chloral, and found that both cis-. and trans-2-oxetanones were
produced in approximately equal amounts. The aldoketenes were
R, R CH-S-CI f ;c = c = o H ' LH
o CC1,-C-H^ — — 3—z
CC1_ Trans 3
generated in situ "by the dehydrochlorination of the appro-
priately substituted acyl chlorides, and/or by dehalogenation
of appropriately substituted «C-haloacyl halides with zinc,
at room temperature.
The isomer distributions were approximately the same, reg-
ardless of the nature of the substituents on the ketene, or
the reaction solvent. A consideration of the principle of the
conservation of orbital symmetry, and the four possible ortho-
gonal approaches led to the conclusion that both isomers of
the 2-oxetanones would be expected to be formed in about equal
amounts, with perhaps a predominance of the cis isomer. A
concerted process was thus suggested for the cycloaddition.
During the course of this investigation, Brady and Smith
found that the generation of dichloroketene by the zinc de-
halogenation of trichloroacetyl chloride in the presence of
acetone and cyclohexanone producted the corresponding 2-oxetan-
ones.
c c l 3 - ^ 0 1 t U S ?
It was proposed that zinc was activating the carbonyl
group of the ketones. This was substantiated by the increased
yield of the cycloaddition of chloral and dimethylketene, in
the presence of activated zinc.
A report (15) since the present investigation was
initiated has revealed that the dehydrohalogenation of cyclo-
heptatriene-7-carboxylic acid chloride in the presence of
benzophenone yields the cycloadduct, containing a conjugated
y-lactone formed by 8 + 2 cycloaddition of 8-oxoheptafulvene
and benzophenone. It was proposed that the y-lactone might
-CI
N(Et) 3-*
0
Ph-B-Ph. & be an isomerized product of the -lactone, the product of
2 + 2 cycloaddition of 8-oxoheptafulvene and benzophenone.
0 |i
Ph-C-Ph
Ph'
2 + 2
& •
Ph
Ph Ph © Ph
8-0xoheptafulvene was also found to react with tropone
to produce the unconjugated y-lactone, the result of a
concerted 8 + 2 cycloaddition.
\]
&7T+ 21r
Recent reviews (23, 9) concerning the chemistry of
2-oxetanones reveal the general instability of this class of
compounds, and the variety of reactions which 2-oxetanones
undergo, such as polymerization, nucleophilic addition
reactions, and decarboxylation. ,
The thermal decarboxylation of 2-oxetanones yields the
expected olefin.
NC = 0 + /
CO,
In 1880 Erlenmeyer (8) proposed that in the preparation
of olefins from the salts of- (3-haloacids, $-lactones of
transitory existence are formed, and then decarboxylate
immediately into olefin and carbon dioxide.
-C-CHp-C-(? S l o w y
i Past \ /
C = C + / N CO,
8
later, in 1883, Einhorn reported (7) that the (^-lactone
derived from f-bromo- $-(o-nitrophenyl) propionic acid
decomposes in boiling water to o-nitrostyrene and carbon
dioxide.
h2£. R.
H
.H '
, c=q CO, H
R = C6H4-o-N02
The thermal decarboxylation of the £-lactone from
5-hydroxy-6-carboxy ^-nor steroids occurs smoothly around
150°C (22).
vo
150° C + CO,
Pr.O
Gresham reported that isovalerolactone in water at
room temperature decomposes rapidly to carbon dioxide and
isobutylene (10), to the near exclusion of hydrolysis. It was
reported that this is probably due to a tendency for ionization
at the tertiary carbon-oxygen bond, with subsequent shift of
electrons, and expulsion of carbon dioxide occuring more
rapidly than attack of an ion at the tertiary carbon.
_H20_ H.
H C—C
^ch3
SCH, CO,
It has "been reported (16) that 2-oxetanones undergo
decarboxylation in boiling water to yield stereoselectively
the corresponding olefins. A competing reaction was the
addition of water to yield the $-hydroxy acid.
Boiling
V *
H > = C
CH y R
75%
/ / H,
R = g6h4-£-ci
CH /
R
SH
80%
H 0 25%
3
00H
COOH
20%
Recently Adam and coworkers have reported (1) the direct
cyclization of f-hydroxy acids with benzenesulfonyl chloride
in pyridine at 0-5°C to tri- and tetrasubstituted £-lactones
in high yields. The $ -lactones obtained decarboxylated at
moderate temperatures of about 140-160°C, into the corres-
ponding olefins, with retention of the initial geometry of the
10
•'C TO X V .thout double bond iso-
H^O-—OH
R ?S ^ R%
>n°o + CO,
r,'°-H4 3
-l comparison ol the relative stability of 2-oxeta.nones
i a v/-i-cn different aiJcyl groups are attached at the ^-carbon
iias sesn ::;ace (14). The rate of decarboxylation of ^-propio-,
P ~ OUXJTO- , and. j'-isovalerolactones in water increased with,
increasing the number of alkyl groups at the p-carbon. This
'VuJ projciDiy due to a greater tendency for ionization to occur
at the carbon and oxygen bond, with subsequent shift of
electrons, and expulsion of carbon dioxide. This would be
expected to occur more readily at tertiary carbon than either
secondary or primary.
CH„ 9 J
H
Cornfortn and coworkers have reported (6) that the
S -lactones obtained from ketene and 0-haloketone and
p -Ii&l0r.iii5ehyde cycloadditions are thermally stable, and
11
do not decarboxylate in water as $-isovalerolactone does, but
gave good yield of corresponding olefin at 150-160°C.
R-CH
1500 0 , H > = o f , + C02
H pH-R
The unusual thermal stability of 4-trichloromethyl-2-
oxetanones have been reported by Oshe (17). It was found
that 4-trichloromethyl-2-oxetanones polymerized upon heating
at 200°C, rather than decarboxylation. However, the nucleophilic
addition such as hydrolysis, alcoholysis, and aminolysis was
200° C (n~0— U - ° ^ ) i i CC1,
n
CC1,
effected in usual manner to give corresponding £-hydroxy
acid, ester, and amide derivatives.
HNu H I 1
I • CC1,
Nu
Nu = OH, OCHj, HNR
12
Brady and Smith havo recently reported (5) thnt attempts
to pyrolyse 3-chloro-4-trichloromethyl-2-oxetanone at 160°C
for 12 hours were unsuccessful; however, 3,3-dichloro-4 ,4-
dimethyl-2-oxetanone decarboxylated at 150°C in the expected
manner, to produce 1,1-dichloro-2-methylpropene.
No Reaction
CI CH_ 15° c > x0 = c'
• \ CI CH,
3
Few 2-oxetanones have "been reported with different
electronegative substituents in the 3- and 4- positions.
Therefore, the effect of such substituents on the ease of
decarboxylation is unknown, although there seems to "be a
very pronounced effect as just described.
In summary, the literature on ketene-carbonyl cyclo-
additions, and decarboxylation of the resulting 2-oxetanones
reveals that (a) the cycloaddition of dichloroketene to
simple ketones is tentative pending further investigation;
(b) very little work has been done with halogenated ketenes;
(c) activation of carbonyl function is necessary for cyclo-
additions in the absence of catalysts; (d) there are no
13
reports on the relative stability of 2-oxetanones, when
different electronegative groups are attached to the -carbon;
(e) the effect of electronegative substituents in oO~P°sition
on decarboxylation of 2-oxetanone is unknown; (f) pyrolysis
of thermally stable 2-oxetanones at higher temperature is
relatively unknown.
Therefore, the purpose of this investigation is threefold;
(1) to examine in detail the cycloaddition of halogenated
ketenes and carbonyl compounds; (2) study the decarboxylation
of the resulting halogenated 2-oxetanones, thus determining
the effect of electronegative substituents at 3- and 4-positions
on the rate of decarboxylation; (3) investigate the effect of
halogens in the halogenated 2-oxetanones on the nucleophilic
addition reaction.
CHAPTER BIBLIOGRAPHY
1. Adam, W. and Baeza, J.t J. Amer. Chem. Soc.. <U. 2000 (1972).
2. Bormann, D. and Wegler, R., Chem. Ber.. 99. 1245 (1966).
3. Bormann, D. and Wegler, R., Chem. Ber.. 100. 1575 (1967). ~
4. Bormann, D. and Wegler, R., Chem. Ber.. 102. 64 (1969). — -
5. Brady, W. T. and Smith, 1., J. Org. Chem.. 36. 1637 (1971). 6 ^
6. Cornforth, R. H., J. Chem. Soc.. 4052 (1959).
7. Einhorn, A., Chem. Ber.. 16, 2208 (1883).
8. Erlenmeyer, H., Chem. Ber.. 13, 303 (1880).
9. Etienne, Y. and Piascher, N., Heterocyclic Compounds Vol. XIX, Ed. Interscience Publishers, Inc., New York, pp. 729-880.
10. Gresham, T. L. and Jansen, J. E., J. Amer. Chem. Soc.. 76, 486 (1954).
11. Hagemeyer, H. J. Jr., Ind. Eng. Chem.. 41, 765 (1949).
12. Hasek, R. H. and Elam, E. U., U. S. Patent 3004989 (1961); Chem. Abstr.. 56, 4623 (1962).
13. F. ?•».?; S. Patent 2356459 (1944); Chem. Abstr. 39, 88 (1945). ; —
14* L i ^ ' Bartlett, P. D., J. Amer. Chem. S o n . . 80t 3885 (1958/•
15. Morita, N. and Kitahara, Y., Tetrahedron Lett.. Q. 872 (1972). ' U
16. f* %a n d Banitt, E. H., J. Org. Chem.. 31,
4043 (1966)*
14
15
18. Quadbeck, G., Angew. Chem. , 68, 361 (1956).
19. Staudinger, H., Chem. Ber. 1355 (1908).
20. Staudinger, H., Chem. Ber. *
1493 (1908).
21. Staudinger, H., Chem. Ber. , 44, 533 (1911).
22. Tull, T. and Ourisson, G., Bull. Soc. Chem.
23. Zaugg, H. E., Organic Reactions, Vol. 8, R. Adams, Ed., Willey, New York, 1954, pp. 305 ff.
n u ' R> rnj,\ R T Kj.i i x i X ,i~ J t J. l , L l
EXPERIMENTAL
Proton nuclear magnetic resonance spectra were obtained
using Jeolco ^iniroar (60 rnHZ) or Jeolco PS-100 (100 mHZ)
spectrophotometers. Chemical shifts are reported v/ith
respect to te tramethylsilane, w M c h was used as an internal
stand<urd. The nmr spectra were recorded at a sample concen-
tration of about twenty percent in carbon tetrachloride,
deuterated chloroform, or deuterated acetone solvents.
The infrared spectra were obtained using a Perkin-Elmer
Model ky7 Grating Infrared spectrometer. The cell used for
sample handling was 0,1 mm fixed pathlength cell with sodium
chloride optics.
Vapor phase chromatography was used for monitoring
reactions, determining the purity of products, and
purification of contaminated products by preparative
chromatographic separation techniques. The instrument used
for analytical purpose was F and K Scientific Model 700,
with a thermal conductivity detection system and a 3% SE.30
on chrornosorb W (AW-DMCS) 80/100-mesh, 5 feet x 0.25 inch
column. For preparative purpose a Varian Aerograph 1520
v/ith a 20 feet x 0,4— inch column v/ith similar column packing
materials was employed.
16
17
Mass spectra were obtained using a Hitachi RMU-6E
mass spectrometer.
Analysis for carbon and hydrogen were conducted by
C.F. Geiger and Associates, Ontario, California.
Preparation of Reagents
All of the solvents employed in this study were
commercially available. The solvents were distilled over
sodium and stored over molecular sieves under nitrogen
atmosphere.
Commercially available triethylamine was distilled
over freshly cut sodium. Technical grade, commercially
available chloral was distilled at 40°C at 80 mm prior to
use. All the carbonyl compounds used in the investigation
were commercially available.
Most of the acid halides were prepared from the corres-
ponding commercially available acid by the following procedure.
One mole of acid was treated with 1.1 mole of thionyl
chloride^ and the reaction mixture refluxed at 100°C for
five to six hours. The acid halides prepared are tabulated
in table I.
cC-Chlorlnation of butanoyl and pentanoyl chloride;
The acid chloride (1.0 mole) and sulfuryl chloride
(1.25 mole) in the presence of 2.0 g of iodine were refluxed
overnight. The fractional distillation of the reaction
mixture gave a 50 per cent yield of 2-chlorobutanoyl chloride
18
"bp 129-131°C (lit. bp 129-131°C (12)), and a 40 per cent
yield of 2-chloropentanoyl chloride, bp 154-155°C (lit. bp
154-155°C (14)).
TABLE I
ACID CHLORIDES PREPARED FROM COMMERCIALLY AVAILABLE ACIDS
Acid Chloride B.P.°C Reference
Butanoyl chloride 110-112 5
Pentanoyl chloride 126-128 5
2-Chloropropanoyl chloride 110-112 11
2-Bromopropanoyl chloride 131-132 8
Chloroacetyl chloride 105-106 17
Dichloroacetyl chloride 108-110 5
Preparation of Bromochloroacetyl chloride
Bromochloroacetyl chloride was prepared by the procedure
of Crompton and coworkers (6) .cc^jJ-Dichlorovinyl ethyl ether
was prepared by adding 650 g (5.0 mole) of trichloroethylene
to a previously prepared solution of 175 g (7.5 mole) of
sodium metal in 3 liters of absolute ethanol, in a flask
fitted with a large reflux condenser. Initially, only a
small portion (50 ml) of trichloroethylene was added, and
the reaction was initiated by heating the reaction flask
to 95°C with a water bath. After the reaction commenced,
19
tile water oath was removed and triehloroethylene added
at sufficient rate to maintain vigorous reflux. After
addition was complete, the reaction mixture v/as allowed
to oxana at room temperature for 10 hours and then poured
into 10 1. of water. The organic layer was separated and
dried over CaCl^. Further drying was accomplished by re-
iluxirig with 1.5 1. of benzene removing the water by azeo-
tropic distillation. The benzene v/as evaporated on the
o
rotatory evaporator and the product distilled, bp 124-126 Cr
and stored over molecular sieves(Linde type 4A). The yield
v/as 400 g (SO per cent).
In a flask fitted with an addition funnel was placed
380 g (2.68 mule) of oc^-diciilorovinyl ethyl ether. A 430-g
(2.70 mole) portion of bromine was added dropwise over a
3-hour period. The bromine was rapidly absorbed as evidence
by the disappearance of the bromine color. After the bromine
addition, the reaction mixture v/as heated strongly under
a stream of nitrogen and the product distilled through a
6-inch Yigreaux column. After about 150 g of ethyl bromide
had been collected at 37-42°C, the temperature rose to 135°C,
and 300 g of bromochloroacetyl chloride were collected from
13S-140°C (lit. bp 138-139°C). This corresponds to a 56 per
cent yield; careful exclusion of atmospheric moisture is
necessary through out the reaction to prevent the formation
of ethyl broraochloroacetate.
20
Activation of Zinc:
A 4-g (0.016 mole) portion of hydrated copper sulfate
was dissolved in 150 ml of water (3), and this solution was
added to 60 g (0.92 g atom) of zinc dust. This mixture was
stirred "by efficient magnetic stirrer for two hours. The
zinc dust was filtered "by suction filtration, washed several
times with acetone, and three times with dry ether. The zinc
was dried in a vacuum oven at 100°C prior to use in dehalo-
genation reactions.
Tri-n-butyltin hydride:
To a stirred slurry of LiAlH^ (4.75 g, 0.136 mole) in
300 ml of anhydrous ether was added 100 g (0.308 mole) of
tri-n-butyltin chloride at such a rate to keep gentle reflux
under nitrogen atmosphere. After addition of tri-n-butyltin
chloride, it was stirred for additional seven hours at 50-60°C.
The excess LiAlH^ was destroyed by addition of water, after
cooling by ice water bath. The reaction mixture was decanted
from lithium and aluminum salts. Distillation under reduced
pressure yielded 70 g (80 per cent yield) of tri-n-butyltin
hyride, bp 68-69°C at 0.3 mm (lit. bp 68-69°G at 0.3 mm (9)).
General procedure for dichloroketene-ketone cyclo-
addition by dehalogenation method:
To a stirred mixture of 3 moles of activated zinc,
200 ml of anhydrous ether and 2 moles of the ketone was
added dropwise an ether solution containing 1 mole of tri-
chlproacetyl chloride at room temperature. Cooling of the
21
reaction vessel was usually necessary, and this was accom-
plished with an ice-water "bath. After the addition was
complete, stirring was continued for an additional hour.
The excess zinc was removed by filtration, and the filtrate
concentrated and extracted three times with dry hexane to
separate the 2-oxetanone from the zinc chloride etherate
and dichloroketene polymer. The hexane extracts were combined,
concentrated, and vacuum distilled to yield the 2-oxetanones.
3,3-Dichloro-4-ethyl-4-methyl-2-oxetanone:
The cycloadduct of dichloroketene and 2-butanone was
prepared in 35 per cent yield; bp 40°C at 0.5 mm; ir,
1875 cm*1 (C=0); nmr, $ 1.1 (t, 3H), 1.72 (s, 3H), 2.08 (q, 2H).
Analysis calculated for CgHgOlgOg! C, 39.3; H, 4.37.
Found: C, 39.08; H, 4.32.
3,3-Diehloro-4-methyl-4-n-propyl-2-oxetanone;
The cycloadduct of dichloroketene and 2-pentanone was
prepared in 35 per cent yield; bp 53°C at 0.5 mm; ir,
1875 cm"1 (C=0); nmr, J 1.1 (t, 3H), 1.78 (a, 3H), 1.5 (m, 2H),
2.0 (m, 2H).
Analysis calculated for C^H^QCO^Og: C, 42.6; H, 5.07.
Pound: C, 42.67; H, 4.96.
3.3-Dichloro-4-methyl-4-iso-propyl-2-oxetanone:
The cycloadduct of dichloroketene and 3-methyl-2-butanone
was prepared in 20 per cent yield; bp 43°C at 0.5 mm; ir,
1874 cm"1 (C=0); nmr, / 1.72 (s, 3H), 1.0 (d, 3H), 1.04
(d, 3H), 2.2 (m, 1H).
22
Analysis calculated for C^H 1 0C1 20 2: C, 42.6; H, 5.07.
Found: C, 42.88; H, 4.88.
3,3-Dichloro-4-chloromethyl-4-methyl-2-oxetanone:
The cycloadduct of dichloroketene and chloroacetone
was prepared in 15 per cent yield; bp 43°C at 0.5 mm; ir,
1880 cm"1 (C=0); nmr, cf 2.0 (a, 3H), 4.25 (s, 2H).
Analysis calculated for C ^ H ^ C l ^ : C, 29.5; H, 2.48.
Found: C, 29.80; H, 2.25.
3* 3-Dichloro-4-benzyl-4-methyl-2-oxetanone :
The cycloadduct of dichloroketene and phenylacetone
was prepared in 40 per cent yield and obtained as a white
solid; mp 80°C; ir, 1870 cm"1 (C=0); nmr, cf 1.55 (s, 3H),
3.0 (d, 1H), 3.35 (d, 1H), 7.1 (a, 5H).
Analysis calculated for C^H^ClgOg: C, 53.88; H, 4.08.
Found: C, 53.67; H, 4.04.
3.3-Dichloro-4--chloroniethyl-4-Phenyl-2-oxetanone:
The cycloadduct of dichloroketene and CJ -chloro-
acetophenone was prepared in 20 per cent yield; bp 125-130°C
at 0.05 mm; ir, 1878 cm"1 (C=0); nmr, / 4.25 (s, 2H),
7.18 (s, 5H).
Analysis calculated for C 1 0H 7C1 50 2: C, 45.2, H, 2.65.
Found: C, 45.02; H, 2.43.
3,3-Dichloro-4.4-dichlororoethyl-2-oxetanone:
The cycloadduct of dichloroketene and sjm-dichloro-
acetone was prepared in 23 per cent yield; bp 85°C at 1.5 mm;
ir, 1882 cm"1 (0=0); nmr, <f 3.9 (s).
23
Analysis calculated for C ^ C l ^ : C, 25.2; H, 1.68.
Found: C, 25.54; H, 1.65.
1,1-Dichloro-2-methyl-1-heptene:
The cycloadduct of dichloroketene and 2-heptanone was
prepared by. the general method indicated above. Prior to
vacuum distillation, the residue revealed a band in the
infrared spectrum at 1870 cm"1 (C=0), verifying the presence
of the 2-oxetanone. However, upon distillation decarboxylation
occurred and the corresponding olefin was isolated in an
over-all yield of 40 per cent; bp 78-80°C at 25 mm; ir,
1635 cm"1; nmr, cf 0.8 (m, 3H), 1.3 (m, 6H), 1.85 (s, 3H)
and 2.25 (m, 2H).
Analysis calculated for CgH^Clgj C, 53.3; H, 7.77.
Found: C, 52.99; H, 7.57.
General procedure for cycloaddition of dichloroketene
and cycloalkanones by dehalogenation method;
To a refluxing stirred mixture of 3 moles of activated
zinc, 200 ml of dry ether, and 1.5 mole of the cycloalkanone
was added dropwise an ether solution containing 1.0 mole of
trichloroacetyl chloride. After the addition was complete,
stirring was continued for four hours. The excess zinc was
removed by filtration and the filtrate concentrated and
extracted with hexane to separate the 2-oxetanone from zinc
chloride etherate and dichloroketene polymer. The hexane
extracts revealed a carbonyl stretching in the infrared at
1872 cm , verifying the presence of the 2-oxetanone. The
24
hexane extracts were combined, concentrated, and vacuum
distilled. Decarboxylation of the 2-oxetanone usually
occurred upon distillation, and the corresponding dichloro-
methylenecycloalkanes were isolated in an overall yield of
40-50 per cent. In those cases where decarboxylation did
not occur, or was incomplete upon distillation, heating at
120-150°C for about one hour was sufficient for decarboxylation.
Dichloromethylenecyclopentane:
Cycloaddition of dichloroketene and cyclopentanone
yielded 3,3-dichloro-1-oxaspiro [3.4~] heptane-2-one in 30
per cent yield; bp 56-58°C at 0.5 mm; 1855 cm"1 (C=0). Upon
heating at 120-150°C for one hour decarboxylation occurred,
to yield dichloromethylenecyclopentane in quantitative
yield; bp 55-56°C at 1.5 mm; ir, 1635 cm"1 (C=C).
Dichloromethylenecyclohexane:
Cycloaddition of dichloroketene and cyclohexanone
yielded 3,3-dichloro-1-oxaspiro [^3.5j octane-2-one in 50
per cent yield; bp 62°C at 0.2 mm; ir, 1850 cm"1 (C=0).
Upon heating at 120-150°C for one hour decarboxylation
occurred to yield dichloromethylenecyclohexane in quantitative
yield; bp 62-65°C at 1.5 mm; ir, 1620 cm"1 (G=C).
3-Me thyldlchlorome thylenecyclohexane;
Cycloaddition of dichloroketene and 3-methylcyclohexanone
yielded 3,3-dichloro-1-oxaspiro [3.5] -5-methyloctane-2-one;
_ 1
ir, 1855 cm (C=0). Partial decarboxylation occurred upon
distillation, and was completed at 120-150°C to yield
25
3-methyldichloromethylenecyclohexane in an overall yield of
45 per cent; "bp 72-75°C at 1.5 mm; ir, 1620 era""1 (C=C).
4-Methyldichloromethylenecyclohexane:
Cycloaddition of dichloroketene and 4-methylcyclohexanone
yielded 3,3-dichloro-1-oxaspiro [ 3.5] -6-methyloctane-2-one;
ir, 1855 cm (0=0). Partial decarboxylation occurred upon
distillation, and was completed at 120-150°C to yield
4-methyldichloromethylenecyclphexane in an overall yield of
50 per cent; bp 70-75°C at 1.5 mm; ir, 1620 cm*"1 (C=C).
Dichloromethylenecycloheptane: HI • inn mm N MI i f KI.I •n,.mi i i I A
Cycloaddition of dichloroketene and cycloheptanone
yielded 3,3-dichloro-1-oxaspiro [3.6] -nonane-2-one; ir,
1865 cm 1 (C=0). Upon distillation complete decarboxylation
occurred and dichloromethylenecycloheptane was isolated in
50 per cent yield; bp 70-72°C at 1.5 mm; ir, 1610 cm"1 (C=C).
Di chlorome thylene cyclo o ctane:
Cycloaddition of dichloroketene and cyclooctanone yielded
3,3-dichloro-1-oxaspiro decane-2-one; ir, 1870 cm"1
(C=0). Upon distillation complete decarboxylation occurred
and dichloromethylenecyclooctane was isolated in 45 per cent
yield; bp 75-78°C at 1.5 mm; ir, 1610 cm"1 (C=C).
Dechlorination of dichloromethylenecycloalkanes:
The dechlorination of dichloromethylenecycloalkanes
was easily accomplished with a slightly modified method of
Boorl and coworkers (1).
The dechlorination was carried out with a 10-12 g atom
solution of sodium in liquid ammonia at -78°C using a
26
dry ice/acetone "bath, an efficient magnetic stirrer, and
dry ice/acetone cold finger.
The required amount of liquid ammonia was charged to the
reaction flask to dissolve the sodium (10-12 g atoms of sodium
per mole of chloride to he dechlorinated). The sodium was
added slowly in small pieces. When the sodium had dissolved,
the dichloromethylenecycloalkanes, diluted with one to five
volumes of dry pentane was added dropwise to the stirred
sodium solution in ammonia and dry pentane. After the addition
was complete, the reaction mixture was stirred for an add-
itional hour to ensure completion of the reaction.
The excess sodium amide was neutralized with slow
addition of solid ammonium chloride until the reaction mixture
became colorless. About 100 ml of water was added slowly and
the cooling hath was removed. The aqueous layer was separated/
and the organic layer was washed with dilute sodium bicarbonate
solution and finally with water. The solution was then dried
over anhydrous magnesium sulfate and the solvent evaporated.
The residue was fractionally distilled to give an 80-90
per cent yield of the methylenecycloalkanes.
Methylenecyclopentane:
Dechlorination of dichloromethylenecyclopentane yielded
methylenecyclopentane in 80 per cent yield? bp 77-78°C (lit.
77-78°C (15)).
Methylenecyclohexane:
Dechlorination of dichloromethylenecyclohexane yielded
27
methylenecyclohexane in 90 per cent yield; bp 100-102°C
(lit. 100-102°C (15)).
3-Methylmethylenecyclohexane:
Dechlorination of 3-methyldichloromethylenecyclohexane
yielded 3-methylmethylenecyclohexane in 90 per cent yield;
bp 123-124°C (lit. 123-124°C (16)).
4-Methylmethylenecyclohexane:
Dechlorination of 4-methyldichloromethylenecyclohexane
yielded 4-methylmethylenecyclohexane in 95 per cent yield;
bp 122-123°C (lit. 122-123°C (16)).
Methylenecjcloheptane:
Dechlorination of dichloromethylenecycloheptane yielded
methylenecycloheptane in 90 per cent yield; bp 136-138°C
(lit. 136-138°C (15)).
Methylenecyclooctane:
Dechlorination of dichloromethylenecyclooctane yielded
methylenecyclooctane in 85 per cent yield; bp 154-156°C
(lit. 154-156°C (15)).
General procedure for cycloaddltlon of alkylhalo-
ketenes with chloral by dehydrohalogenation;
A solution of 2 moles of freshly distilled chloral
in 150 ml of hexane was stirred while 1 mole of oC -halo-
acid chloride and 1.5 mole of triethylamine were added
simultaneously at room temperature. After stirring for an
additional hour, the salt was removed by suction filtration,
and the filtrate concentrated. Distillation under reduced
28
pressure afforded the corresponding 2-oxetanone in good yields.
3-Chloro-3-methyl-4-trichloromethyl-2-oxetanone '•
2-Chloropropanoyl chloride was dehydrochlorinated in
the presence of chloral to give 53 per cent yield of the
2-oxetanone. Both isomers were obtained in approximately
A 1
equal amounts; bp 70 C at 0.5 mm; ir, 1875 cm" (C=0); nmr,
S 2.05 (s, 3H), 4.95 and 5.18 (2 s of cis and trans isomer, 1H).
Analysis calculated for G^H^C1^02: 0, 25.21; H, 1.67.
Found: C, 25.53; H, 1.51.
3-Chloro-3-ethyl-4-trichloromethyl-2-oxetanone:
2-Chlorobutanoyl chloride was dehydrochlorinated in
the presence of chloral to give a 50 per cent yield of both
isomers of the 2-oxetanone; bp 72-75°C at 0.5 mm; ir,
1875 cm"1 (C=0); nmr,cf 1.23 (t, 3H), 2.5 (m, 2H) and 4.82
and 5.18 (2 s of cis and trans isomers, 1H).
Analysis calculated for CgHgCl^Ogi C, 28.57; H, 2.38. Found: C, 28.52; H, 2.33.
3-Chloro-3-n-propyl-4-trichloromethyl-2-oxetanone:
2-Chloropentanoyl chloride was dehydrochlorinated in
the presence of chloral to form a 45 per cent yield of the
2-oxetanone. Both isomers were formed in approximately
equal amounts; bp 72-78°C at 0.5 mm; ir, 1875 cm"1 (C=0);
nmr, cf 1.0 (m, 3H), 1.7 (m, 4H), 4.82 and 5.18 (2 s of cis
a n d "trans isomers, 1H).
Analysis calculated for O ^ H g C l ^ : C, 31.57; H, 3.00.
Found: C, 31.61; H, 3.05.
29
3-Bromo-»3--niethyl~4-trichlorometh,yX-2-oxetanone:
2-Bromopropanoyl chloride was dehydrochlorinated in
the presence of chloral to give a 60 per cent yield of both
isomers of the 2-oxetanones; hp 75-80°C at 0.4 mm; ir,
1875 cm"1 (C=0); nmr, cf 2.2 (s, 3H), 4.8 and 5.22 (2 s of
els and trans isomers, 1H).
Analysis calculated for C^H^BrC1^02: C, 21.27; H, 1.52.
Pound: C, 21.26; H, 1.65.
Methylhaloketene cycloadditlons with o-chlorobenz-
aldehyde:
A one-mole portion of the 2-halopropanoyl chloride was
added dropwise at room temperature to a stirred solution
of 2 moles of triethylamine, 200 ml of hexane, and 1.5 mole
of o-chlorobenzaldehyde. After the addition, stirring was
continued at room temperature for four hours. The amine salt
was filtered, the filtrate concentrated, and the residue
vacuum distilled to yield the 2-oxetanones.
3-Ghloro-3-methyl-4-o-chlorophenyl-2-oxetanone:
2-Chloropropanoyl chloride was dehydrochlorinated in the
presence of o-chlorobenzaldehyde to yield two isomers of the
2-oxetanone in about equal amounts, yield 45 per cent; bp
50°C at 0.2 mm; ir, 1878 cm"1 (C=0); nmr, cf 2.2 and 2.38
(2 s of cis and trans isomers, 3H); 6.35 and 6.45 (2 s cis
a n d trans 1H); 7.0 (m, 4H).
Analysis calculated for C^HgClgOg: C, 51.95; H, 3.28.
Pound: C, 51.53; H, 3.34.
30
3-Bromo-3-methyl-4-o-chlorophenyl-2-oxetanone:
2-Bromopropanoyl chloride was dehydrochlorinated in
the presence of o-chlorobenzaldehyde to yield two isomers
of 2-oxetanone in about equal amounts, yield 50 per cent;
bp 125-13O°0 at 0.1 mm; ir, 1878 cm"1 (C=0); nmr,/ 2.1
and 2.7 (2 s for cis and trans 3H); 7.0 (m, 4H).
Analysis calculated for C.jQHgBrC102: C, 43.6; H, 2.93.
Found: C, 43.91; H, 2.92.
Methylhaloketene cycloaddition with sym-dichloro-
tetrafluoroacetone:
A solution of 1 mole of triethylamine in 200 ml of hexane
was cooled to -78°C, and then 1 mole of 2-halopropanoyl
chloride was added dropwise. After the addition was complete,
the reaction mixture was stirred at this temperature for 15-20
minutes, and then 1.5 mole of sym-dichlorotetrafluoroacetone
was added..After warming to room temperature, the salt was
removed by filtration, the filtrate concentrated, and the j i;
residue vacuum distilled to yield the 2-oxetanones.
3-Chloro-3-methyl-4.4-bis(chlorodifluoromethyl)-ji
2-oxetanone:
2-Chloropropanoyl chloride was dehydrochlorinated in
the presence of sym-dichlorotetrafluoroacetone to give a
55 per cent yield of the 2-oxetanone; bp 48-50°C at 1.5 mm;
ir, 1885 cm"1 (C=0); nmr,<f 2.05 (s).
Analysis calculated for CgHjCl^F^OgJ 0, 24.82; H, 1.08.
Found: C, 24.94; H, 1.03.
31
3-Bromo-3-methyl-4>4-bis(chlorodifluoromethyl)-2-oxetanone:
2-Bromopropanoyl chloride was dehydrochlorinated in
the presence of sym-dichlorotetrafluoroacetone to give a
60 per cent yield of the 2-oxetanone; bp 48-52°C at 0.5 mm;
ir, 1885 cm~1(C=0); nmr, 6 2.08 (s).
Analysis calculated for CgH^BrC^Og! C, 21.56; H, 0.99.
Found: C, 21.38; H, 0.96.
Cycloaddition of chloroketene with sym-dichloro-
tetrafluoroacetone:
The same procedure was employed for this cycloaddition
as described above for the methylhaloketenes with this
ketone, yield 50 per cent; bp 45-47°C at 1.5 mm; ir, 1895 cm
nmr, </ 5.25 (s).
Analysis calculated for C^HCl^F^Og: C, 21.81; H, 0.37.
Found: C, 21.79; H, 0.69.
3,3-Dichloro-4-trichloromethyl-2-oxetanone:
A solution of 2 moles of freshly distilled chlora.1 in
150 ml of hexane was stirred while 1 mole of dichloroacetyl
chloride and 1.5 moles of triethylamine were added simul-
taneously at room temperature. The salt was removed by
filtration, and the filtrate was concentrated. Distillation
at ,90°C at 12 mm afforded 60 per cent yield of 2-oxetanone:
ir, 1870 cm"1 (C=0) (2).
3,3-Dichloro-4-acetyl-4-meth.yl-2-oxetanone:
A solution of 1.5 mole of triethylamine in 300 ml of
hexane containing 1.5 mole of dimethylglyoxal was stirred
32
while a solution of 1 mole of dichloroacetyl chloride in
hexane was added at room temperature. After completion of
the addition, the reaction mixture was stirred for four
hours and filtered. The solvent was removed under reduced pres-
sure and the 2-oxetanone distilled at 85°C at 3 mm in 40
per cent yield; ir, 1870 cm"*1 (C=0); nmr, & 1.85 (s, 3H)
and 2.4 (s, 3H).
Analysis calculated for C^HgClgO^: C, 36.58; H, 3.08.
Found: C, 36.33; H, 2.92.
Bromochloroketene-aldehyde cycloadditions:
The same procedure was employed as described for
3,3-dichloro-4-acetyl-4-methyl-2-oxetanone.
3-Bromo-3-ch.loro-4-phenyl-2-oxetanone:
Bromochloroacetyl chloride was added to a solution
containing henzaldehyde and triethylamine. Prior to vacuum
distillation the residue revealed a "band at 1870 cm"1 and
a singlet at <f 5.66 and a singlet at cf 6.0 in equal amounts
for the methinyl hydrogens for "both isomers. Upon distillation
decarboxylation occurred, and ^-"bromo-^-chlorostyrene was
isolated in 35 per cent yield at 80°C at 0.5 mm; ir,
1600 cm"*1; nmr, cf 6.95 and 7.05 (2 s of cis and trans
isomers, 1H) and 7.25 (m, 5H).
Analysis calculated for CgHgBrCl: C, 44.14; H, 2.75.
Pound: C, 44.18; H, 2.61.
3-Bromo-3-chloro-4-isopropyl-2-oxetanone:
Bromochloroacetyl chloride was dehydrochlorinated in
the presence of isobuytraldehyde. Vacuum distillation
33
afforded a 20 per cent yield of two isomers in equal amounts
at 60°C at 0.5 mm; ir, 1872 cm-1 (C=0); nmr, 1.15 (d, 6H),
1.93 (m, 1H), 4.26 and 4.40 (2 d for cis and trans isomers, 1H).
Analysis calculated for CgHgBrC102: C, 31.63; H, 3.43.
Found: C, 31.23; H, 3.41.
3-Bromo-3-chloro-4-trichloromethyl-2-oxetanone:
Bromochloroa,cetyl chloride was dehydrochlorinated in
the presence of chloral to produce the 2-oxetanone in a 50
per cent yield of two isomers in equal amounts at 65-70°C
at 0.5 mm; ir, 1880 cm"1 (C=0); nmr, 5.42 and 5.61 (2s
for cis and trans isomers).
Analysis calculated for C HBrCl/jC>2: C, 23.52; H, 0.53.
Found: C, 23.38; H, 0.61.
trans~3-Chloro-4-trichloromethyl-2-oxetanone:
The in situ cycloaddition of chloroketene and chloral
at room temperature gave both cis and trans isomers of
2-oxetanone; cis isomer, pair of doublets centered at 5.18
and 5.58 (J=6 Hz); trans isomer, pair of doublets centered
at 5.04 and 5.25 (J=3 Hz). The cis/trans ratio in the
reaction mixture was 1.64 (4). The following prodedure
yielded only the trans isomer.
A solution of 1 mole of triethylamine in 200 ml of
hexane was cooled to -78°C in dry ice/acetone bath and then
1 mole of chloroacetyl chloride was added dropwise. After the
addition was complete, the reaction mixture was stirred at
this temperature for ten minutes and then 1.5 mole of chloral
34
was added. After warming to room temperature, the salt was
removed by filtration, and the filtrate concentrated, and the
residue vacuum distilled to yield only trans-3-chloro-4-tri-
chloromethyl-2-oxetanone in 40 per cent yield; nmr, pair of
doublets centered at J 5.04 and 5.25 (J=3.0 Hz); ir, 1870
cm""1 (C=0).
Dechlorination of 3,3-dichloro-4-ethyl-»4-methyl-
2-oxetanone by tri-n-butyltin hyride:
A solution of 0.05 mole of freshly distilled tri-n-
butyltin hyride in hexane was slowly added to a stirred
solution of 0.05 mole of 3,3-dichloro-4-ethyl-4-methyl-2-
oxetanone in hexane. The reaction solution was kept cool by
cold water. After stirring for two hours, the hexane was
evaporated under reduced pressure, and the residue distilled
at 40-43°C at 1.5 mm to give 3-chloro-4-ethyl-4-methyl-2-
oxetanone in quantitative yield. Both cis and trans isomers
~ 1
were obtained in approximately equal amounts; ir, 1865 cm
(C=0); nmr, cT 1.0 (t, 3H), 1.5 (2 s of cis and trans isomers,
3H), 1.80 (m, 2H) and 4.92 (s, 1H).
Analysis calculated for CgH^ClO^ C, 48.48; H, 6.66.
Pound: C, 48.36; H, 6.53.
4-Ethyl-4-methyl-2-oxetanone:
A solution of 0.05 mole of tri-n-butyltin hydride in
hexane was added to a solution of 0.025 mole of 3,3-dichloro-
4-e thyl-4-methyl-2-oxetanone and 0.1 g of azobisisobutyro-
nitrile in hexane. The reaction solution was cooled by cold
35
water. After stirring for two hours, the solvent was
removed under reduced pressure, and 4-ethyl-4-methyl-2-
oxetanone was distilled at 60-65°C at 10 mm in quantitative
yield, (lit. 60°C at 10 mm (10)).
Decarboxylation
Decarboxylation of 4-ethyl-4-methyl, 3-chloro-4-ethyl-
4-methyl and 3«3-dichloro-4-ethyl-4-methyl-2-oxetanones:
Three solutions of 1.5 g of 2-heptanone containing
1.5 g of each 2-oxetanone in three 10 ml flasks were decarbo-
xylated at 80°C in an oil bath. The rate of decarboxylation
was determined by observing the disappearance of the 2-oxe-
tanone carbonyl band in the ir at about 1865-70 cm~^. The
carbonyl band of 2-heptanone at 1735 cm was used as an
internal standard. The relative rates were determined from
the time required for 50 per cent decarboxylation. The
relative rates for 4-ethyl-4-methyl, 3-chloro and 3»3-dichloro-
4-ethyl-4-methyl-2-oxetanones were 100 ; 6 : 1 respectively.
Decarboxylation of 3,3-dichloro-4-ethyl-4-methyl, 3,3-
dichloro-4-chloromethyl-4-methyl and 3,3-dichloro-4,4-dichloro-
methyl-2-oxetanones;
A 3 g portion of each of the 2-oxetanones in three 10
ml flasks were thermally decarboxylated at 150°C in an oil
bath. The rate of decarboxylation was determined by vpc
analysis by observing the disappearance of 2-oxetanone and
appearance of the olefin. The time required for 50 per cent
36
decarboxylation was found and the relative rates for
3,3-dichloro-4-ethyl-4-methyl, 3,3-dichloro-4-chloromethyl-
4-methyl and 3,3-dichloro-4,4-dichloromethyl-2-oxetanones
were 100 : 17 : 1 respectively.
Attempted decarboxylation of 3»3-dichloro-4-ethyl-4-
methyl-2-oxetanone in water:
A 5.0 g portion of the 2-oxetanone was mixed with 50
ml of water in a 100 ml flask. The flask was heated to 50°C
in an oil bath for about thirty minutes. No evidence of
olefin was detected on vpc.
Decarboxylation of 3.3-dichloro-4-acetyl-4-methyl-2-
oxetanone and 3.3-dlchloro-4-chloromethyl-4-methyl-2-oxetanone:
A 3.Q g portion of each of the 2-oxetanones were thermally
decarboxylated at 170°C in an oil bath. The rate of decarbo-
xylation was determined by vpc analysis by observing the
disappearance of 2-oxetanone, and' appearance of the olefin.
The relative rates were found to be approximately 1 ; 1.
Pyrolysis of 3-chloro-3-methyl-4-trichloromethyl-2-
oxetanone:
A 24 g (0.1 m) portion of the 2-oxetanone was pyrolyzed
in a ketene generator at 1.5-2 mm as the 2-oxetanone was
slowly refluxed over the electrically heated red hot filament.
After about 2 hours, trichloromethylallene was isolated from
a dry ice-acetone trap in the system. Distillation afforded
9.4 g (60 per cent) of the allene at 80-82°C; irf 1610 cm"1
(vs) and 1965 cm"1 (w); nmr, <f 5.36 (d, 2H) and 6.03 (s, 1H).
37
Analysis calculated for O ^ C l ^ : C, 30.47; H, 1.94.
Found: C, 30.32; H, 1.99. (Mol. wt. 156 by mass spect#f
theory 156).
Pyrolysis of 3-chloro-3-ethyl-4-trichloromethyl-2-
oxetanone:
A 10-g portion of the 2-oxetanone was pyrolyzed in a
ketene generator as described above, 1,1,1-trichloro-2,3-
pentadiene was obtained in 50 per cent yield. Purification
was accomplished by preparative vpc; ir, 1600 cm"1; nmr,
S 1.75 (d, 3H), 6.12 (q, 1H) and 6.32 (s, 1H).
Analysis calculated for C^H^Cl^: C, 34.98; H, 2.90.
Found: C, 35.16; H, 2.79 (Mol. wt. 170 by mass spect.,
theory 170).
Pyrolysis of 3-chloro-3-propyl-4-trichloromethyl-2-
oxetanone:
A 9.0-g portion of the 2-oxetanone was pyrolyzed in a
ketene generator under the same conditions described above.
The 1»1»1-trichloro-2,3-hexadiene was obtained in 40 per
cent yield and purified by preparative vpc; ir, 1600 cm'1;
nmr,J 1.0 (t, 3H), 2.13 (m, 2H), 6.08 (t, 1H) and 6.22 (s, 1H).
Analysis calculated for C ^ C l ^ C, 38.81; H, 3.77.
Found: C, 38.66; H, 3.65. (Mol. wt. 184 by mass spect.,
theory 184).
Pyrolysis of 3,3-dichloro-4-trichloromethyl-2-oxetanone:
A 26-g (0.1 m) portion of the 2-oxetanone was pyrolyzed
under the same conditions as described above. The products
38
of the pyrolysis were collected in a dry ice-acetone trap _ <4
at -78 C. There was a strong band in the ir at 1962 cm"
at low temperature, which disappeared upon warming to room
temperature. Distillation afforded 7.5 g (35 per cent) of
1,3,3,3-pentachloropropene, 1.7 g (13 per cent) of tri-
chloroethylene, and 1.8 g (11 per cent) of perchloroallene
dimer, which crystallized from the residue of the disti-
llation; mp 90-91°C (lit. 90-91°G (13)). The ir spectrum
was identical to that reported in the literature.
Pyrolysis of 1,1,3,3.3-pentachloropropene:
Pyrolysis of 5.0 g of 1,1,3>3»3-pentachloropropene
under the identical conditions as described above for
3,3-dichloro-4-trichloromethyl-2-oxetanone at 25 mm pressure
produced products in the dry ice-acetone trap, which gave _ -i
a band in the ir at 1962 cm at low temperature, which
disappeared upon warming to room temperature.
Decarboxylation of trans-3-chloro-4-trlchloromethyl-
2-oxetanone:
A 20-g (0.09 mole) portion of the 2-oxetanone was
pyrolyzed in a ketene generator under reduced pressure as
described above. A 13 g (80 per cent) portion of 1,3,3,3-
tetrachloropropene was isolated from the dry ice-acetone
trap. This olefin consisted of approximately equal amounts
of the els and trans isomers as evidenced by the nmr coupling
constants for the vinyl protons (7).
39
Nucleophilic Addition
2.2-Dichloro-3-hydroxy-3-methylpentanoic acid:
3.3-Dichloro-4-ethyl-4-methyl-2-oxetanone (0.05 mole)
was stirred with 100 ml of water at 60-65°C. After 4 days,
the organic layer was separated from the aqueous layer.
Vpc analysis of the organic layer revealed some decarboxy-
lation product along with the starting 2-oxetanone. The
aqueous layer was slowly evaporated and the hydroxy acid
crystallized in a 15 per cent overall yield; mp 82°C; ir,
1722 cm"1; nmr (deuterated acetone), j 1.0 (t, 3H),
1.5 (s, 3H), 1.80 (m, 2H)» 2.2 (m, 1H).
This acid was converted to the corresponding methyl
ester.
Methyl 2,2-dichloro-3-hydroxy-3-methylpentanoate:
3,3-Dichloro-4-ethyl-4-methyl-2-oxetanone (0.05 mole)
was added to a stirred 50-ml portion of methanol at 50°C.
The progress of the reaction was followed "by vpc. After 48
hours, only 50 per cent of the starting 2-oxetanone had
disappeared and the corresponding ester formed. Fractional
distillation afforded the ester at 53-54°C at 0.25 mm; ir,
1720 cm"1; nmr (deuterated acetone), <f 1.0 (t, 3H), 1.45
(s, 3H), 1.85 (q, 2H), 3.8 (s, 4H).
Analysis calculated for C^H^ClgO^: C, 39.90; H, 5.59.
Pound: C, 39.72? H, 5.62.
40
N,N-Dimeth.yl-2,2-dichloro-3-hydroxy-3-methylpentanamide:
3,3-Dichloro-4-ethyl-4-methyl-2-oxetanone (0.05 mole)
was added to a stirred solution of dimethylamine (0.06 mole)
in 100 ml of ether at 0-5°C. Upon warming to room temperature,
the ether was evaporated and the amide distilled in quanti-
tative yield at 70-75°C at 0.5 mm; ir, 1640 and 1670 cm*"^;
nmr (deuterated acetone), cf > 3H), 1.45 (s, 3H),
2.0 (q, 2H), 3.25 (m, 6H), 4.65 (s, 1H).
Analysis calculated for CQH15C12N02: C, 42.11; H, 6.58.
Found: 0, 42.61; H, 6.62.
2,2, 4.4» 4-Pentachloro-3-hydroxy"butanoic acid;
3,3-Dichloro-4-trichloromethyl-2-oxetanone (0.05 mole)
was stirred with 100 ml of water at 70°C. After 2 hours,
the organic layer had gone into solution. The water was
slowly evaporated and the acid crystallized from solution
in 80 per cent yield; mp 180°C; ir, 1725 cm"^; nmr (deuterated
acetone), <f , 2.2 (s, 1H), 5.2 (s, 1H).
Analysis calculated for C^H^Cl^O^: C, 17.36; H, 1.08.
Found: C, 17.31; H, 0.98.
Methyl 2,2,4,4.4-Pentachloro-3-'hydroxy"butanoate:
3,3-Dichloro-4-trichloromethyl-2-oxetanone (0.05 mole)
was slowly added to a stirred 50-ml portion of dry methanol
at room temperature. The reaction was exothermic and upon
evaporation of the solvent and distillation of the residue,
there was obtained a quantitative yield of the ester, bp
100°C at 0.05 mm; mp 72°C; ir, 1740 cm~^; nmr (deuterated
41
acetone), / , 3.92 (s, 3H), 5.2 (m, 1H), 7.1 (m, 1H).
Analysis calculated for C ^ C l ^ : C, 20.65; H, 1.72.
Found: C, 20.23; H, 1.65.
N.N-Dimethyl-2,2,4,4,4-pentachloro-3-hydroxybutanamide:
3,3-Dichloro-4~trichloromethyl-2-oxetanone (0.05 mole)
was added to a stirred solution of dimethylamine in 100 ml
of ether at -78°C. Upon warming to room temperature, a
small amount of amine hydrochloride precipitated from
solution. The reaction mixture was filtered and the ether
evaporated to yield the crystalline amide, mp 123°C; ir,
1635 and 1670 cm**''; nmr (deuterated acetone), cf , 2.0 (s, 1H),
3.1 (s, 6H), 5.4 (s, 1H).
Analysis calculated for CgHgCl^NOg: C, 23.72; H, 2.63.
Pound: C, 23.53; H, 2.71.
CHAPTER BIBLIOGRAPHY
1. Boord, C. E., Hoff, M. C. and Greenlee, K. W., J. Amer. Ghem. Soc., 73, 5329 (1951)/
2. Borrmann, D. and Wegler, R., Chem. Ber., 99, 1245 (1966). ~
3. Brady, W. T. and Liddell, H. G., J, Org. Chem., 31, 626 (1966).
4. Brady, W. T. and Smith, L., J. Org. Chem., 36_
1637 (1971). ^
5. Brown, H. C., J. Amer. Chem. Soc., 60^ 1325 (1938).
6. Crompton, H. and Vanderstichele, P., J. Chem. Soc., or UJ, 691 (1949).
7. Fields, R. and Hasteldine, R. J. Chem. Soc., (C) 165
0969).
8. Fischer, E. and Raske, K., Chem. Ber. 39, 3981 (1906).
9. Ghosez, L. and Montaigne, R.., Tetrahedron, 27, 615
(1971).
10. Hagemeyer, H. J. Jr., Ind. Eng. Chem., 41 , 765 (1949).
11. Michael, A., Chem. Ber. 34, 4028 (1901).
12. Paal, C. and Schiedewitz, H., Chem. Ber., 62, 1935 ( 1929 ) . ~
13. Roedig, A., Bischoff, F,, and Markl, G. Justus Liebigs Ann. Chem., 6^0, 8 (1963).
14. Servais, L., J. Chem. Soc. ,Ab3tr., 1_1J, 80 (1901).
15. Siegel, S. and Dunkel, M., J. Org. Chem., 31. 2802 (1966). - ~
16. Vilkas,,M. and Abraham, N., Bull. Soc. Chim. France.. 201, 1196 (1960).
17. Wilde, P., Justus Liebigs Ann. Chem.. 132, 171 (1864).
42
CHAPTER III
RESULTS AND DISCUSSION
. The generation of dichloroketene "by the zinc dehalo-
genation of trichloroacetyl chloride in the presence of
simple ketones resulted in the formation of the corresponding
2-oxetanone. The cycloadducts were prepared in 15-40 per
cent yields, aa illustrated in Table I,
9 R
CCl,-b-Cl + ^ C = 0 3 R
Ether
Dichloroketene does not undergo cycloaddition with
simple ketones when the ketene is prepared "by the triethyl-
amine dehydrochlorination of dichloroacetyl chloride (1).
However, if zinc/zinc chloride are added to the dehydro-
halogenation mixture, cycloaddition occurs in about 15 per
cent yield. Thus the role of zinc/zinc chloride was activating
the carbonyl group of the ketone.
Unfortunately, this method cannot be used to effect the
cycloaddition of dichloroketene and simple aldehydes. The
aldehydes trimerize in the presence of the activated zinc
43
44
TABLE I
2-0XETAN0NES PROM DICHIOROKETENE-KETONE
CYCLOADDITIONS
R R' % Yield
Me Et 35
Me n^Pr. 35
Me i-Pr 20
Me CH2CI 15
Me CH2-Ph 40
Ph CH2CI 20
CH2CI CH2CI 23
45
and zinc chloride.
R—I—H ZS(?"C12—>• n u n _ Ether
Also, efforts to cycloadd dichloroketene to ^^-unsatu-
rated aldehydes and ketones, such as crotonaldehyde, cinnam-
aldehyde and methyl vinyl ketone were unsuccessful. Such
carbonyl compounds are deactivated "by the conjugated double
bond. However, the zinc dechlorination of trichloroacetyl
chloride in the presence of cyclic ketones resulted in the
formation of the corresponding 3,3-dichloro-spiro-2-oxetanones.
CI CI
(CH ) n \o + CCl3-?-Cl (CH2)n
n = 4, 5, 6, 7.
These cycloadditions ultimately lead to an important
method for the synthesis of dichloromethylenecycloalkanes
and methylenecycloalkanes.
The exocyclic olefins are generally prepared by the
Wittig reaction. Aside from this well known reaction, which
has its limitations, little information on other methods
is available in the literature.
46
( C H2)n
Ph
CHL=P-Ph 2 i
Ph ^ C ^ n ^ ) ~ C s
H Ph
0=P-Ph i Ph
2-0xetanones are generally quite susceptible to decar-
boxylation to olefins when heated (10). The higher the
boiling points of these cycloadducts the more this decar-
boxylation becomes significant. The cycloadduct of dichloro-
ketene and 2-heptanone could not be isolated by vacuum
distillation because decarboxylation occurred. However, the
olefin was isolated in 40 per cent yield based on trichloro-
acetyl chloride.
CI
A ci
R = -(CH2)4-CH3.
C= C CH,
R CO,
Likewise, the spiro-2-oxetanones obtained from dichloro-
ketene and cycloalkanones are easily decarboxylated upon
distillation, or heating, yielding the dichloromethylene-
cycloalkanes in 40-50 per cent yields, based on the tri-
chloroacetyl chloride.
47
CI CI
(cH2)n
A - ( o h a ~ ^ ) / C 1
=c + ecu CI *
The dechlorination of the dichloromethylenecycloalkanes
with sodium in liquid ammonia at -78°C afforded the methylene-
cycloalkanes in near quantitative yields.
"0" \
,C1
CI
Na/NH, -78° 5 >
These dichloroketene cycloadditions are accompanied
by the formation of an insoluble tar which is attributed
to polymerization of the ketene, hence the lower yields on
cycloadditions. This is characteristic of reactions involving
halogenated ketenes.
Halogenated ketene-olefin cycloadducts can be readily
dehalogenated with tri-n-butyltin hydride, or with zinc-
acetic acid to the parent ketones (4), (8).
48
i n ^ 4 V 3 £ 2 l * o r
Zn/HOAc.
Similarly, cycloadducts of dichloroketene and simple
ketones can be dehalogenated. The removal of one chlorine
from 3,3-dichloro-4-ethyl-4-niethyl-2-oxetanone occurs
readily with a 1 : 1 mole ratio of tributyltin hydride and
cycloadduct, but the removal of both halogens requires the
addition of a free radical source such as azobisisobutyro-
nitrile in an excess of tri-n-butyltin hydride.
(n-C4H0)3SnH >
Et
The cycloaddition of alkylhaloketenes with chloral,
o-chlorobenzaldehyde and sym-dichlorotetrafluoroacetone
was investigated and the results are shown in Table II. The
ketenes were generated in situ by the triethylamine dehydro-
chlorination of the appropriate eC-haloacid chlorides.
TABLE II
2-OXETANONES FROM METHYLHALOKETENE-CARBONYL
COMPOUND CYCLOADDITIONS
49
R-CH-ti-Cl- + ^C=0 R
R
Bf R R " X % Yield
cci3 H Me CI 53
coi3 H Et CI 50
CC1, H n-Pr CI 45
o-ClPh H Me CI 45
cf2CI cf2ci Me CI 55
cci3 H Me Br 60
o-ClPh H Me Br 50
cf2ci C P2 C 1 Me Br 60
50
Ar. exacinati on of the car'oonyl compounds in Table II,
aloi".£ with the fact that propionaidehyde, her.zaldeh.jde, acetone,
oyclohexanone and ethyl methyl ketone did not enter into
cyclooedition vdth the niethylhaloka tenes under the conditions
employed, reveals that activation of the carbonyl group is
necessary for cycloadditicn.
Cycloadditions of the alkylhaloketenes with chloral
and o-cnlorobenzaldehyde can produce cis and trans isomers.
, o p , \ R-CH-C-Cl + )C=0 •• 5~>
H A
cis trans
Both c.ls and trans isomers were produced an approximately
equal amounts as previously reported, for the aldoketenes
and chloral. The isomer distributions were determined as
ratios of integrated peak areas on gas chromatograms of the
reaction solutions, and by nmr integration of the methinyl
.region.
Also, the cycloaddition of bromochloroketene with chloral,
henzaldehyde and isobutyraldehyde produced cis and trans
isomers of 2-oxetanones in approximately equal amounts.
"Bromochloroketene was generated in situ by the dehydro-
chlorination of bromochloroacetyl chloride with triethylamine.
51
o R JtSr-CH-C-Cl + VC= 0
I '
CI H
G1
Br
H H cis trans
The isomer distributions obtained from the cycloaddition
of several different ketoketenes with different aldehydes
reveal that the reaction is not stereoselective. Like the
aldoketene-chloral cycloadditions (3)» this cycloaddition
is concerted and a consideration of the four possible
orthogonal approaches, leads to the conclusion that both
isomers would be expected to be formed in about equal amounts.
Since all the halogenated ketenes are not stable, they
are trapped by in situ methods of dehydrohalogenation of
appropriately substituted acid halides having «c-hydrogens.
Tertiary amines, notably triethylamine, have been used as
dehydrohalogenating agents.
^ \ ?« ^ ^CH-C-Cl + NCEt)^ * ' C " C — 0 + HN(Et),Cl
X X •>
The ketene-carbonyl cycloadditions are found to be
catalyzed by Lewis acid type catalyst (6). However, this
catalyst cannot be employed in the ketene-carbonyl compound
52
cycloadditicm reactions when ketene is generated in situ
by the dehydrohalogenation method, since tertiary amines,
used to effect the dehydrohalogenation would neutralize the
Lewis acid catalyst. Thus the halogenated ketene-carbonyl
compound cycloaddition is limited to the activated carbonyl
compounds, which would condense in absence of catalyst.
The generation of ketenes by the triethylamine dehydro-
halogenation method can present serious competing reactions;
e.g., reaction of the amide with the activated carbonyl
compounds. Triethylamine was found to react with sym-dichloro-
tetrafluoroacetone. This problem was alleviated by a stoichio-
metric reaction of the amine and acid halide at low temperature
in the absence of the sym-dichlorotetrafluoroacetone. and
then this reactant was added as the reaction mixture warmed
to room temperature.
^CH-b-Cl + N(Et)3 • 7 8 ° C >
R = CF2C1
; 8 e X
„CH-ij-iHEt),
Cl e '
0
R-C-R
2 5°C R
R
The order of the addition of reagents is very important
as the addition of triethylamine to the oc-haloacid chlorides
results in the formation of ®c-halovinyl esters, (2) of the
acid chlorides. Furthermore, since triethylamine catalyzes
the polymerization of chloral, these cycloadditions were
53
fIR- C~X K(nt; 0 - 0 . X X
I 0 i U
R-CH-C-X -> 0=0-0-0-014?,
X ! !
X X
aecompiisned oy separate out simultaneous addition of the
.nali.de ana amine xo chloral in the solvent.
The dehydr-ochlorination of chloroacetyl chloride in
the presence of £vm-dichlorotetrafluoroacetone at -78°0
.'ecru '"Ited in the formation of the adduct derived from chloro-
Ice ten e.
ch2CI-<3-CI _1) N(3t) 7 at -78° 2) R-C-R"' *
5 oi
+ HN(Et), i J 01
The in situ cycloaddition of chloroketene and chloral
at room temperature produces both cis and trans isomers as
previously described (3). However, if this reaction is
conducted at -78 0 and slowly allowed to warm to room
9 o , , CH9-C-C1 + 001v-0-K - l i M I ^ 25°c 01
3->
001
cj s
001.,
trnnn
54
temperature, only the tram? isomer is produced.
Qu HI , at/"-CM-\ _0Clv~0-.fi 0 if
9C1-C-01 + N(Et),, ^ -78UC
H
However, this is not a general result as "both isomers
were obtained in ketoketene cycloadditions with chloral in
approximately equal amounts regardless of the temperature.
Also, other aldoketenes gave a mixture of isomers even when
prepared by this method.
Decarboxylation
The effect of halogen in the 3-position of 2-oxetanones
upon the rates of decarboxylation was easily determined by
comparing the rates of decarboxylation of the compounds in Table
III. The relative rates represent the time required for 50 per
cent decarboxylation. The decarboxylation was measured by
observing the disappearance of the carbonyl band of
- 1
2-oxexanone at 1870 cm in the infrared using the carbonyl
band of the solvent, 2-heptanone, as an internal standard.
A further comparison of the effect of chloro substituents
in the 3-position was observed; when 3,3-dichloro-4-ethyl-
4-methyl-2-oxetanone did not decarboxylate in water up to
50°C, whereas isovalerolactone (4,4-dimethyl-2-oxetanone)
55
readily decarboxylated in water at room temperature (5).
2-Heptanone „ R V = < " e + 00
80 C R Et 2
TABLE III
R R' Relative Rate
CI CI 1
H CI 6
H H 100
Similarly, the effect of a chloromethyl substituent
in the 4-position on the rate of decarboxylation can he
seen by comparing the rate of decarboxylation of the compounds
in Table IV.
Again, the relative rates represent the time required
for completion of 50 per cent of the decarboxylation. The
rate of decarboxylation was measured by observing the
disappearance of 2-oxetanones and appearance of olefins
by vpc.
56
15G°C 01N R
G=C ci' R
CO,
DA BIS IY
R
CH:2CI
c h 2 c i
CH-
R
CHgCl
CH-
CH0CH~ d 0
Relative Rate
1
17
100
The rate of decarboxylation of the 2-oxetanones derived
from dichloroketene and chloroacetone and dimethylglyoxal was
compared at 170°C, and the rates were approximately the same.
G H 2 G 1 Me-0=0
The attainment of a conjugated system in the transition state of
3,3-d ichloro-4-acetyl-4-methyl-2-oxetanone upon decarboxylation,
serves as a driving force for the decarboxylation. This ease
57
of decarboxylation was also observed when the 2-oxetanone;
obtained from brorr.ochloroketene and benzaldehyde and iso-
buiyraldehyde were prepared.
?h isoPr.
3-3ror,o-3-ch 1 oro-4-pheny 1 -2-oxetanone could not be
distilled under reduced pressure, as decarboxylation occurred
at 100°C to yield the corresponding styrene derivative,
while 3-bromo-4-chloro-4-isopropyl--2-oxetanone could be
isolated, and did not appreciably decarboxylate prior to
160°C. Both isomers of 3-brouio-3-chloro-4-isopropyl-2-oxe-
tanone were produced in the cycloaddition reaction in
approximately equal amounts.
The decarboxylation of the 2-oxetanones derived from
methylch1oroketene and chloral, p-chlorobenzaldehyde and
sym-aichlorotetrafluoroacetone did not occur up to
250°C. Polymerization of these 2-oxetanones was observed
at higher temperature, as reported by Ohse and coworkers (7).
O
n H CEU 250 0 , _ • i 3
— > — c — G — c ~ ~ ) i i ji n CClv 0
3
58
Thus, the halogen substituents on the 2-oxetanone ring
severely inhibits the decarboxylation. This is perhaps an
indication of the mechanism of the elimination reaction#
and suggests some charge separation in the transition state
between the carbon and oxygen bond, whereby the 4-carbon
assumes some positive character.
+ 00 0 / N C.
Decarboxylation of the cycloadducts of alkylchloroketene
and chloral did decarboxylate over an electrically heated
wire, but this decarboxylation was accompanied by a dehydro-
chlorination to yield trichloromethyallenes in 40-60 per
cent yields.
* , C = C = C + HC1 + CO, A H ^CC13
R = H, Me, Et.
No evidence of the halogenated olefin was found in any
of the systems. A consideration of the order of the two
elimination steps suggest that the dehydrochlorlnation
precedes the decarboxylation. Since the °C-chlorine is more
59
i a ;> ilr, sirliyc! rorh'l o r.i na I i on o ,i" tiic i'-oxc lauonc j mo re
likely to lead to the 2-oxetanone intermediate, which would
be expected to decarboxylate more readily than the 2-oxetanone,
Furthermore, if decarboxylation occurred first, it is less
Ly to expect the olefin to undergo dehydrochlorination. 1 - Is* -J. J V - ^
HCl j R s
CGI.
•GO, /H c = c= c
H/ CC15
CC1.
The 2-oxetanone obtained from dichloroketene ana chloral
was likewise very resistant to decarboxylation. However,
refluxing 3,3-dichloro-4-trichloromethyl-2-oxetanone over
an electrically heated wire produced a mixture of products
including the expected olefin, 1,1,3,3,3-pentachloropropene,
perchloroallene, the allene dimer and trichloroethylene.
-CO
A 2->
CI v ,H -HCl
CI s CC15 A
CI ^C = CS
CI CI
C1S ,ci c = c = c
CI NC1
Cl-C
60
The perchloroallene was observed in a dry ice acetone trap
- 1
as evidenced "by a "band in the infrared at 1962 cm . This
band disappeared upon warming to room temperature but the
allene dimer was isolated (9).
The olefin resulting from decarboxylation was isolated
in 40 per cent yield, and suggests that the decarboxylation
preceded the dehydrochlorination. This is substantiated by
the fact that the olefin, 1,1,3,3,3-pentachloropropene,
dehydrochlorinates under the reaction conditions to yield
perchloroallene^, which dimerizss upon warming to room tempera-
ture .
Cl s 01 s ,C1 C — C — c = C= C y dimer
CI xcci3 A c l ' V
C 1
The cycloadduct obtained from chloroketene and chloral,
was also quite resistant to decarboxylation. However, de-
carboxylation did not occur as above but the corresponding
olefin, 1,3,3,3-tetrachloropropene, was produced in 80 per
cent yield. A trace of allene (trichloroallene) was observed
in the cold trap at -78°C as evidenced by a band in the
infrared at 1962 cm . However, this was a much weaker band
than in the previous system. This decarboxylation was
conducted on the trans-2-oxetanone and an equal mixture of
61
the two isomeric olefins was obtained.
01 x ,001- H v ,001-C — C v ^ + 0 = 0 3
w w / \ H H 01 H
cis trans
Thus it is very apparent that any electronegative
substituent on the 2-oxetanone ring decreases the rate of
decarboxylation. The presence of a trichloromethyl substi-
tuent on the 4-position of the 2-oxetanone ring severely
inhibits decarboxylation. Decarboxylation of the alkyl-
chloroketene-chloral adducts over an electrically heated
wire provides a useful synthesis for these exotic trichloro-
methylallenes.
Nucleophilic Addition
The reaction of 3,3-dichloro-4-ethyl-4-raethyl-2-oxe-
tanone with water, methanol and dimethylamine produced the
corresponding ^-hydroxy acid, ester and amide.
ch3 o
+ HNu * CH3-CH2-C—CC12-B-NU
OH
Nu a OH, OMe, NMe2
62
The reactions paralleled the nucleophilicity of the
nucleophiles; e.g., dimethylamine gave a quantitative yield
at 0-5°C, methanol a 50 per cent yield after 48 hours at
50°C, and water a 15. per cent yield after 4 days at 60-65°C,
Some decarboxylation accompanied the hydrolysis reaction.
The reaction of 3,3-dichloro-4-trichloromethyl-2-oxe-
tanone with the same nucleophiles also occurres to yield
only the acyl-oxygen cleavage products as illustrated.
HNu CCl,-CH-CCl0-C-Nu 3 i 2 A '
OH
Nu = OH, OMe, NMe2
This 2-oxetanone is considerably more reactive than
3,3-dichloro-4-ethyl-4-methyl-2-oxetanone. 3,3-Dichloro-4-
trichloromethyl-2-oxetanone reacts with dimethylamine at
-78°C, and upon warming to room temperature a quantitative
amount of amide is produced. There is some indication of
nucleophilic displacement of a halogen as evidenced "by some
dimethylamine hydrochloride. 3,3-Dichloro-4-trichloromethyl-
2-oxetanone reacts with methanol at room temperature to
immediately produce a quantitative yield of ester, and with
water at 70°C in two hours to produce an 80 per cent yield
of hydroxy acid.
63
The exclusive acyl-oxygen cleavage with the two halo-
genated 2-oxetanone investigated is probably the result of
the electronegative substituents increasing the electro-
philicity of the carbonyl carbon atom. The increased reactivity
of 3, 3-dichloro--4-trichloromethyl-2-oxetanone, and the exclusive
aeyl-oxygen cleavage of the trichloromethyl-2-oxetanones
studied by Ohse and coworkers (7) is probably due to the
trichloromethyl substituent stabilizing the negative charge
on oxygen in the transition state.
Conclusions
Dichloroketene cycloaddition to simple ketones provides
a useful synthesis of a series of halogenated 2-oxetanones
and methylenecycloalkanes. In the preparation of dichloro-
ketene by the zinc dehalogenation of trichloroacetyl chloride,
the zinc/zinc chloride are acting as catalyst for dichloro-
ketene-ketone cycloaddition. Cycloaddition of alkylhalo-
ketenes with unsymmetrical carbonyl compounds produce cis
ana trans isomer of 2-oxetanones in approximately equal
amounts. Activation of the carbonyl compounds is necessary
for cycloaddition.
Electronegative substituents on the 2-oxetanone ring
decrease the rate of decarboxylation. However, if conjugation
results from decarboxylation, this seems to serve as a
driving force for the elimination and decarboxylation occurs
more readily than expected. The presence of a trichloromethyl
64
substituent on the 4-position of the 2-oxetanone ring
severely inhibits decarboxylation. This is perhaps an
indication of the mechanism of the elimination reaction and
suggests some charge separation in the transition state,
whereby the 4-carbon assumes some positive character. De-
carboxylation of the alkylchloroketene-"chloral adducts
over an electrically heated wire provides a useful synthesis
for these exotic trichloromethylallenes.
Electronegative substituents on the 2-oxetanone ring
increase the reactivity of the 2-oxetanone towards nucleo-
philic addition, and only acyl-oxygen bond cleavage occurs
during the nucleophilic addition reaction.
CHAPTER BIBLIOGRAPHY
1. Bormann, D. and Wegler, R., Chem. Ber.f 102, 64 (1969).
2. Brady, W. T., Parry, F. H., Roe, R., Hoff, E. F. and Smith, L., J. Org. Chem., 35, 1515 (1970).
3. Brady, W. T. and Smith, L,, J. Org. Chem., 36, 1637 (1971).
4. Ghosez, L. and Montaigne, R., Tetrahedron, 27, 615 (1971). ~
5. Gresham, T. L. and Jansen, J. E., J. Amer. Chem. Soc.,
76, 486 (1954).
6. Hagemeyer, H. J. Jr., Ind. Eng. Chem., 41 , 765 (1949).
7. Ohse, H. and Palm, R., Monat. Chem., 98, 2138 (1967).
8. Rey, M., Huber, U. A. and Dreiding, A. S., Tetrahedron Lett., 3583 (1968).
9. Roedig, A., Bischoff, F., and Markl, G. Justus Liebigs Ann. Chem., 670, 8 (1963).
10. Zaugg, H. E., Organic Reactions, Vol. 8, R. Adams, Ed., Willey, New York, 1954, pp. 305 ff.
65
BIBLIOGRAPHY
Books
Etienne, Y. and Fiascher, N., Heterocyclic Compounds Vol, XIX, Ed. Interscience Publishers, Inc., New York, pp. 729-880.
Zaugg, H. E., Organic Reactions, Vol. 8, R. Adams, Ed., Willey, New York, 1954, pp. 305 ff.
Articles
Adam, W. and Baeza, J., J. Amer. Chem. Soc.. 94. 2000 (1972). ' ~ —
Boord, C. E., Hoff, M. C. and Greenlee, K. W., J. Amer. Chem. Soc.» 73, 3329 (1951).
Bormann, D. and Wegler, R., Chem. Ber.. 99, 1245 (1966).
Bormann, D. and Wegler, R., Chem. Ber.. 100, 1571 (1967).
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The following articles appeared from this investigation:
Brady, W. T. and Patel, A. D., J. Heterocycl. Chem., 8j 739 (1971).
Brady, W. T. and Patel, A. D., J. Chem. Soc. D, 1642 (1971).
Brady, W. T. and Patel, A. D., J. Org. Chem. 37, 3537 (1972).
Brady, W. T. and Patel, A. D., Synthesis, 565 (1972).