w4o-4ozO/n 53.00+ .Q) 0 19aaRrpmonhap&

THE BROMINATION OF 3-8RoMO-6,7-BENZOBICYCLO~~.2.I~~TA-2.6-~IENE

AND CHARACTERIZATION OF THE PRODXTS

Hetin Balci. and Mansur Harmandar'

Faculty of Science, Department of Chemistry, AtatUrk University, Erzurum/Turkey

Sumary: The bmmination of 3-brcmo-6,7-benrabicyclo [3.2.0 octa-2,6diane at -50°C has been found to give only one product, the tribrwidc 8 producei via WdcJl,8P,,dW"Oi,, S.?,ZTd,,g~t With dCcoDprnylng Uyl rigrdtfon. mhe bromind-

tion at O°C producd nbhrtirrangad trfbromfdes beside tha reuunged tribro- aide dnd the ketoD 12. The structures of the products wdre d8tmaincd by IH-, 13C-MfR dam and. gingh X-r& JtruCturdl MdlySiS. The addftipn wcbamsrr, is discussed in tcrhs # cro- and endo-dttack.

INTRODUCTION

Recently, we reported our initlal results' on the addition of bromine to 3-bromo-6,7-bentobicyclo-

[3.2.flocta-2,6-dfmc (1) in connectibh tith our work on bicycllc allenes'. In this paper we dcs-

cribc the full characterization of these products and their spectroscopic properties.

1 2a R=fI R’=cH3 3 3

2b R-S,b(CCR3)2 R'=CH3

2c R=!&6,7,&(F)q R'=CH3

It has been shown that electrophillc addition to bicyclic systems such as (2) and (3) can lead to

a multiplicity of products'. Attack on the double bond may be endo or exo. The intermediate may re-

act with nucleophiles to give nonrearranged products or undergo Wagner-tieemin rearrangement ln-

volving either aryl group or alkyl bridge before reacting to give rearranged products (Scheme 1).

Paquette et al.' have studied the photooxygenation. oxywrcuratlon and hydroboration of three dlf-

ferently substltiuted 2-methylbenzobicyclo[2.2.2~octadienes (2). Syn stereoselectivity was obser-

ved in every case. Electronic interactions in these molecules were explored by photoelectron spec-

troscopy and WWO/3 calculations. These ctiined tools served to show that through-space interac-

tion is absent in these molecules. Smith et al .‘ have observed similar results by epoxidation of

benzobicyclop.2.2]octadlene systems. They found that m-chloroperbenzoic acid reacts in mcthylene

chloride. acetonitrlle, primarily with syn-attack. However, in oxygen containing solvents (diethyl

ether, ethyl acetate) the rate of the reaction was considerably decreased but the stereochemistry

3645

M. BALCI and M. HARNANDU

of the reagent changed in favor of the formation of the sterically less favored anti-cpoxidcs. The

enhanced stereoselectivity of the peracld was discussed in tenns of home-conjugation in the transi-

tion state being important in determining the product selectfvlty. Mre recently, Smith' has stud-

ied the addition of bromine to 5.8-diacetoxy-1.4-ethanonaphthalene (4) and obtained only one pro-

duct (5). Clearly attack of bromine has occured from the sterically less favored side of the double

bond with subsequent aryl migration.

OAC OAc 4 5

RESULTS AND DISCUSSIONS

3-8romo-6.7-bentobicyclo~.2.l]octa-2,6-diene (1) was prepared by the publIshed method' and sub-

jected in CHC13 to bromination at O°C and -5OOC. Suprisingly, we obtaIned a completely different

product distribution. From the reaction at -5OOC we tsolated a single tribromide (8) in quantitative

yield. While 90 Hit lH-hMR spectrum clearly showed the tree methine protons and two A8-systems, suc-

cessful analysls of the stereochemistry of the brcvnlne even with the aid of proton drcoupllng was

not possible. 13C-t8fR data was consistent with the proposed structure showing 6 aliphatfc carbons

and 6 arowtic carbons' (Table 1); On the basis of these data the correct configuration of (8) could

not be established.

Therefore, the product was subjected to single-crystal X-ray analysis which revealed the compound

to be (1SR. 4SR, 10RS)-2,2.lO-trlbr~-1.2.3,4-tetrah~ro-l,4-ethanonrphthalene (8)' (Ffgure 1).

It is evident from the bromine configuration in (8) that the initial attack by the bromine has

occurred fran the sterically less favored side of the n-system. There Is no questlon that the hyd-

rogen aton of the methano bridge can provfde suf-

ficient bulk to divert an incuning bromide pref-

erentially away from the exo-face to the double

bond. Hmtever, the fact that we obtained only the

rearranged product shows that this effect is clearly

not overwhelming. The homoconjugative interaction

between the developing cationic center and the aryl-

n-electroncenter plays an important role in promo-

ting attack from the Tess favored side of the double

bond. This reasoning explains the sole formation of

(8). In the case of endo attack we should expect

rigwe 1. X-r8y cry8td 8ttuctur8 of 8. either unrearranged products (9 and 10) or products

involving alkyl bridge shift.

The bronination of 1 at O°C was suprising. The 'H-MR studies revealed that the reaction mixture

was very complex. After repeated column chromatography we isolated six products, the identification

of which was no trivial task. As a major product we isolated 8 +n a yield of 42%. 8 and 11' were

identified by comparison of the spectroscopic data with those of authentic salpples. The structures

of 9 and 10 were determined on the basis of spectral data. The 'H- and 13C-tMR spectrrrm pattern of

9 was very similar to that of 10 which indicates that they are stereoisomers. The protons on the

bridging methylene group (C,) in 9 and 10 gave rise to an AB-system whose internal proton (H8i) is

further coupled with the adjacent bridgehead protons where the external proton (H&) does not show

any measurable coupling with bridgehead protons H, and H5. Inspection of Dreidings models indicates

that the dihedral angle between Hgt and bridgehead protons H, and H5 is near 90' and dihedral an-

gle between Hsi and bridgehead protons is near 20-30'. An interesting feature of these AB-systems

fs the chemical shift differences (M 0.55 ppn) between the external bridge protons Hs, in 9 and 10.

There is no considerable chemical shift difference between the resonances of internal hydrogens in

9 and 10 (in both cases the splitting pattern of the A&system remained). Hs, in 10 resonates at

higher field compared to Hs, in 9. This observation can be explained on the basis of strong sterlc

interaction between the proton H& in 9 and the nelgbboring broraine in the exo-position. Any steric

repulsion between %e in 9 and the gninal bromines at C3 is out of the question due to the chair

conformatfon of the cyclohexane rfng. It is well known that interactions related to the van der

Yaals effect causes a paramagnetic contribution to the shielding constants which results in a shift

to lower field'. This observation strongly supports the configurational assigmmnt of 9 and 10. This

finding was also supported by the 13C-llM chemical shifts. In saturated open-chain and cyclic systems

the steric effect on carbon shfelding is observed when two hydrogenated carbons are y-gauche relative

to each other". Typical y-gauche effects are observed in configurationally rigid systems such as

methylcyclohexanes" and nethylnorbornanes'O. Other substltuents, e.g. halogens ra4,ses the y-effect

to -7 ppn.

'Ii- and

13C-NMR

Chemical Shifts

Aromatfc

Olcfinlc and

1 2

3 4

5 01

6,

Protons

Amnatic

Carbons

Coupling Constants

(Hz)

3.6 dd

6.88 dd

----

4.8 d

3.9 ID

2.6 dt

2.3 d

7.4-6.5 m 151.76 141.07

J,,-7.0, J,~=2.1,'J1b-1.0

140.41 127.16

J

.J

56.16.

so.45

37.93

126.91 125.21

ISi see m4.4

42.87

120.02 121.54

J,ire-10.4

4.15 d

----

2.8-3.65 3.0 I

4.0-4.4

2.0-2.45 I W6J

7.0-7.4 o 140.35 136.98

M-system

ddd

128.46 127.21

125.69 124.51

59.58

58.38

55.81

u.95

3.7 t

5.15 dd

----

3.1 I

3.2 m

2.45 dtt 2.7 d

7 . 1 br . , 36.52

34.27

' 144.26 143.95

50.08

63.01

62.41

49.41

41.41

41.11

128.32 127.47

124.17 124.06

7.2-7.5 m 143.81 139.92

128.21 127.31

125.43 123.90

4.35 t

----

6.85 dd

3.9 dt

4.1 p

-cH

2-pr

oton

s 7.1-7.4 a 141.41 139.86

2.45-1.9 AD-

133.94 127.04

46.11

42.51

57.46

Sys

taa

ddd ddd

125.94 124.10

37.94

123.76 122.97

3.64 t

4.45 t

----

5.42 d

3.75 t

2.58 ddt

2.93 d

7.45 m

141.91 141.31

f,,=3.2

Jbs=J.O

7.25 .

126.98 126.49

-J

-4.6

51.40

193.71

57.60

46 19

50.59

126.47 124.20

J1.i

,@i

49.67

J

-12.0 J

8ei

bai =2.3

Br

Table

1. 400

IwHr 'tl- and

100 Mz

13C-NMR

Spectra

of the compounds

8, 9, 10,

11,

12. and

13 i

n CDC13.

Brominatiooof3&wn& ,7-bcnzobicycloI3.2,I)octr-Z.(idrmt 3649

The steric perturbation of the C-H bond involved causes the charge to drift towards carbons; the

bonding orbitals at carbon expand and shielding will arfst. The brfdging carbons in 9 and 10 are rt-

sonatlng at 41.11 pprn and 47.16 ppm, respectively. Thtrefort, the high fitld resonance at 41.11 ppm

was assigned to the rrthylcne carbon CR in 9 uhtrt the bromlnt atom ts Vi the exo-position. Other

chemical shifts (see Tablt 1) were also consistent with tht proposed structures 9 and 10. Finally

the correct conflguration of the exo-isaner (9) was assigned by X-ray crystallographic analysis"

(Fig. 2). The position of the bromine in 9 could also be established by means of chem(cal reactions.

Treatment of (8) with one mol potassfum ttrt. butoxlde gavt the known exo-dlbromide (11).

33.90

In additfon to the products mentfoned above we isolated one more polar product tn a yield of 3%.

The IR showed a carbonyl group. The mass spectrum (n+ 338/340/342) and analysis of the lH- and '3C-

lt4R spectra Indicated the presence of two bromlnt atoms. 13C-NMR data were consistent W.th a c3.2.1]-

bicyclic structure shoutng 5 aliphatic carbons, 6 aromatic carbons and one carbonyl carbon. The

stereochemistry assigned to 12 hes an exptrfmental baste fr#r its 400 MHz 'ti-!W in the 6 2.5-3.0

region. The bridgt protons at C9 In 12 appear as an AB-system. B-part (t&) shows a doublet. There

Is no further coupling with the adjacent bridgehead protons H, and H6. Howcvcr. the A-part (high

field resonance) fs split into triplets of doublets of doublets. Triplet splitting arises from the

hydrogens at bridgehead Hl and H6. Doublet splftting ('J.low coupling constant) originates fram the

proton on C4 which is in the en&?-posftlon. In the cases of '3 ~Jw speaks of the N or 6 Y arrange-

ment. In the bicycllc systems 12 the bonding arrangement of the coupled protons meets the H crite-

rion, For the assignnnt of the stereochemfstry In isonrrfc endo- and exo-bicyc~oheptane deriva-

tives the magnitude of 'J is of importance, since only the endo proton couples with the anti brfdgt

protons.

3650

?fqure 2. x-ray crystal structure of 9. ligure 3. x-ray crystd strvctum of 12.

The fact that the internal bridge proton (H8,) shows a long range coupling with only one proton

(H4) Indicates that th;3stemochemistry of the bromine atoms in 12 am different. As-try fn the

molecule supported by C-M establishes unambiguously the exo- and endo-orientation of the bro-

mlne atoms. Flnally X-ray structure analysts of 12 confirms the structural findings" (figure 3).

The mechanism for formation of the dibromo ketone 12 is glven below. Ye assume that the dibromide

11 is a secondary product formed by addition of bromine to 1 to give 9 followed by hydrogen bmmide

ellmlnation. The reaction of 11 with bmmlne“' gives the tetrabrom, compound 14 which hydrolyses on

silica gel during column chromatography to give 12 (Scheme 4).

In conclusion; we obtalmd a different product dlstribution in the reaction of bromine with 1

at O'C. We assume that 8, 9, and 10 are primary products. The formation of both stereoisomers 9

and 10 does not give any indication of tiich of the two competing modes of endo- and exo-attack is

preferred, since both isomers can be forrrd from endo-attack as well as exo-attack as shown below

(Scheme 5). The fact that we did not observe any trace of alkyl shift products supports the exclu-

slve fonnatlon of the exo-bmmonium Ion. The different product dlstribution at O°C results from

at c2 ‘e% C-1 ni Br Br

10 scnmm 5

the life time of the interardlate 6. At -Soot the life time of the intezuediate is increased so that the rearraflgrrnt can take place completely. However, at O°C brunlne ion can attack the ero-intenae-

dlate before rearrangamnt since the lffe time of the intermediate is decreased.

EXPERIMENTAL SECTION

General. Melting points were determined in open capillary tubes and are uncorrected. Infrared spec-

tra were obtained from KBr pellet on a Perkln Elmer 337 Infrared Recording Spectrophotometer. The

RI@l spectra were recorded with EM 360 Vat-fan Spectrometer and 8ruker 400 Miz Spectrwmater. Mass

spectra were recorded on a Finnigan-MT m Model 4000 mass spectrometer at an ionizing voltage 70

eV. Analytical thin-layer chromatography (TLC) was performed on silica gel 60,,, plates. Column chro-

matography was done on silica gel (60-200 mesh) from Merck Chemical Company.

Bromination of 1. (lSR.4SR.10RS)-2.2.1O-Tribromo-l,2,3.4-tetrahydro-l,4-ethanonaphthalene 8.

a) at -5OOC

To a solution of 5.0 a (15.9 nsnol) of I in 100 mL of CH,Cl, was added droowise. with sti.rina and during 1 h a solution of 2.6 g (16.25 owl) of bromine lnL25LmL of CH Cl ai -5O'C. The reaction nix- ture and l'J

as allowed to stir for 2h at -5OOC and the solvent was removed y iWo tary evaporation. The 'ti- C-H(R of crude material indicated that only one product was formed quantitatively. Analytical

pur;e sample was obtained by crystallization from n-hexane, np; lOl-102oC. MS, m/e 392/394/396/398 (M 11%). 313/315/317 (M'-8r, 22). 234/236 (M'-28r, 10 cm-l) 3075, 3045. 3020. 2980. 1480, 1455. 1255, 1100, 1

, 207/209 (19). 153 (22 1 , 128 (100). IR (K8r.

Calcd.: 025, 955, 850, 765. Ana . C,2H,,Br3 (395.41).

C, 36.46, H. 2.81, Br, 60.63. Found: C, 36.41. H, 2.91, Br. 60.98.

b) at O°C To a solution of 3.0 g (9.55 mnol) of 1 in 100 mL of CH2C12 was added dropwise. and with stirring

a solution of 1.6 g (10.0 nrnol) of bromine in 25 mL of CH2Cl lowed to stir for 2h at O°C and the solvent was removed unde F

at O°C. The reaction mjxture w~jc~& reduced pressure. The H- and

spectra of crude material indicated the existence of a complex mixture. Crude product was charged over a silica gel (150 g) column. Elution with petroleum ether furnished as first fraction the tri- bromide 9.

(lRS.2RS,5RS)-2,3,3-Tribromo-6,7-benzoblcyclo-[3.2.l]oct-6-ene 9. mp 105-106°C (from n- hexane). 1140 mg (222). MS, m/e, 392/394/3%/398 (H*). IR (KBr, cm-l) 3070, 3050. 3020, 2970, 2950. 1470, 1460. 1430. 1170. 1150, 945. Anal. C12H118r3 (395.41) Calcd.: C. 36.46, Ii, 2.81, Br, 60.63. Found: C, 36.32, H. 2.88, Br, 60.42.

Continued elution with the same solvent afforded as second fractfon the dibromide 11. (lRS.2RS,5RS)-2.3-Dlbromo-6.7-benzobicyclo-[3.2.l]octa-3,6-dlene 11. 450 mg(ll2) recrystallized from n-hexane. Comparison of the spectral data of this comoound with those reported in the litera- ture' were in full agreement.

As third fraction we isolated the dlbrcmide 13". (lSR,4RS,5RS)-2.10-Dibromo-l,4-dlhydro-lz~-ethanonaphthalene 13. mp 80-81°C, 155 mg (3.9 I) from CHCl /petroleum ether (1:6). IR (KBr. cm ) 3060. 2970. 1610, 1470. CIS. m/e. 312/314/316 (8:). 208/306 (100). 153 (49). Anal. C,2H,08r2 (314.03) Calcd.: C, 45.89, H, 3.21, Br. 50.90. Found:C, 46.13, H. 3.25, Br, 50.63.

As forth fraction we isolated the tbibraide 8. those obtained by the reaction at 0 C.

2130 mg (42.21). This product was identical with

Further elution with petroleum ether furnished 10. (lRS,2SR.5RS)-2.3,3-Trlbromo-6,7-benzob~cyclo~.2.~octd-ene 11. mp 16g-17?°C, 440 mg (8.7X) from CH C12/petroleum ether (1:4). HS, m/e, 392/394/396/398 (H'). IR (CHCl , cm' ). 3070, 3050, 3020, 29g0, 1430, 1355, 1295, 1250, 1230, 1195. 1120. Anal. C12H118r3 (395.21) Calcd.: 8r. 60.63. Found: C, 36.71, H, 2.95, Br, 60.03.

C, 36.46, H, 2.81.

Finally, elution with CH Cl /petroleun ether (1:') gave as last fraction 12. (lRS.2RS.4RS,5SR)-2.4-Di&o&-3 -oxo-6.7-benzobicyclo@.2.Ooct-6-ene 12. mp 128-13O'C. 290 mg

(ti-2Br, 83). ?51 (go), 128 (75). 115 (100). IR (CHCl (6.9%) from CH Cl2/petroleum ether (2:'). MS, m/e, 328/330!!32 (g, 3%). 249/251 (W-dr, 68). ;;fl

. C&ib08r20 (330.03) Calcd.. ) 2980, 2920, 1720, 1470, 1455

C, 43.67, H. 3.05. Br, 48?;3:0. 4.85. Found: C, 43.45. H, 3.15. Br, ’

Reaction of g with potassium tert.-butoxide.

To a solution of 450 mg (1.14 nsnol) of 9 in 10 ml of abs. THF was given t-BuOK (190 mg. 1.71 rmnol) and the resulting mixture was refluxed for 3 h under nitrooen. After coolina to ram temoerature water was added and aqueous phase was extracted with n-hetine (2x50 ml). and the carbineh hexane ex- tracts was washed with water, dried, filtered and evaporated in vacua. The crude product was crystallized from n-pentrne which was identical with this obtained by dibromocarbene addition to benzonorbornadiene and bromination of 1 as second fraction. 225 mg (771).

3652 M. Bmand M.-M

ACKNOWLEDGEMENT: The authors are fndcbtcd to AtdtUrk Univeristy (6rant 1986/7) for ffnancial support of thls work and wish to express their appwc4ation to Prof. E. Vogel, Dr. H. Sctmlck r (University of Cologne). Prof. Dr. H, Gunther and Dr. II. Yesscner (University of Sisgch) for \r,_ fUR and Mass spectral measurements and to Mr. Sahmettin Vlldrt for technical asststance.

REFERENCES

11 21 31

41

51 6) 71 81 9)

101

11)

12) 131 141 151

Department of Chsmfstry, Faculty Of Educatfon, At&&k Unlvorrity, Erzurum. Turkey. M. tiarmnndar, II. Balcl, Tetrahadron Let&, 26. 5465, 1985. al fl. Balcl, tA. Harffk%?dar, Ymtrdwdran Lett., 25. 237, 1984.

bf tL Balci, W.fl. Jones. J. A& C?aaw Sot., 103, 2674, 1981. c) t?. Balc2, W.& Jones. J. Al. Che6. Sac., 102, 7607. 1960. al N.N. Provolotskaya, 1.1. Llmasova. E.T. Barus, 0. Exner, V.A. Esrkhsrh, J. Org. Cbr. WXxf4

Engl. Transl.1 39. 2264, 1969. bl S.J. Cristol. R.C. Kochsnsky, J. Org. CM%. 40, 2171. 1975. cl W.B. Smith. .7. Org. C%m., SO. 5731, 1985. L.A. Psquette, F. Bellany, G.J. Wells, R.C. 96hm, R. Gleiter. J. Am. Cbuu. Sot.. 103, 7122, 1981. W.B. Smith, L. Stock. S.J. Cornforth, ~etrabsdron, 39. 1379, 1963. K.

a. M. al b) cl 41 bl Cl

0. 0.

Kitshonoki, Y. Takano, A. tlatsuura. K. Kotera, Tetrahedron, 25, 335, 1969. Ergln. ?I. Harmandar. II. Belcl. Acta Cryst. C43, 1621, 1967. Gilnther, l NRR Spectroscopy’ John Ulley, 813, 1960. O.K. Oalllng. 0.m. Grant, J. Am. chm. Sot., 89, 6612, 1967. A.S. P&in, 6. Casu. H,J. &OCh, CaO. J. fh=., 48, ms, im.

D.E. Donnsn, J.D. Roberts, J. Am. QIeie. Sot.. 92, 1355, 1970. H.J. Schneider, I?. Price, T Keller, Angew. Chm., 63, 759, 1971. E. Breltmalor. G. Brsuw, “13 C-NM Spektroekople” Georg Thiarm Verlsg, Stuttgart. 54. 1677. E. Breitmsler. W. Vosltor, “13C-NflR Spectroscopy*, nDnographs In i?odPrn Chemiety 5. edited by H.F. Ebel, Verlag Chamie. Weinhaim, blew York 1978. BGyJkgJngBr, fl. Harw!.¶ndar, Il. BSlcl, submitted for publication.

BGyUkgGngBr, to be published. __ Independent reaction of lSOlet8d 11 with bromine followed by SlO COlum chromstography geVe 12. The dibromids 13 was also synthesixed independently by tiBr elin&tiOn of 6 u8fng 008 equtvalent potassfum tort.-butoxfde.