baeyer-villiger oxidation: mechanism and enantioselective systems
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Literature Meeting. Baeyer-Villiger Oxidation: Mechanism and Enantioselective Systems. Jean-Nicolas Desrosiers January 31, 2005. Outline. 1. Introduction 2. BV mechanistic studies 3. Enantioselective reactions 3.1 Seminal work by Strukul and Bolm 3.2 Katsuki's systems - PowerPoint PPT PresentationTRANSCRIPT
Baeyer-Villiger Oxidation:Mechanism and Enantioselective Systems
Jean-Nicolas Desrosiers
January 31, 2005
Literature Meeting
Outline
1. Introduction
2. BV mechanistic studies
3. Enantioselective reactions
3.1 Seminal work by Strukul and Bolm
3.2 Katsuki's systems
3.2.1 Bidentate ligands
3.2.2 Multidentate salen ligands
The Discovery of the Baeyer-Villager Oxidation
K2S2O8 + H2SO4 + H2O 2KHSO4 + H2SO5
Heinrich Caro in 1898
NH2H2SO5 NO2
Adolf von Bayer & Victor Villiger in 1899
O
O
Menthone
Carvomenthone
H2SO5
H2SO5
O
O
O
O
Caro, H. Angew. Chem. 1898, 845.
Baeyer, A.; Villiger, V. Ber. Dtsch. Chem. Ges. 1899,32, 3625.
Well-Known and Widely Applied ReactionO
R1 R2
O
R1 OR2
[O]
[O]
O O
O
R1, R2 = alkyl or Ar
[O]
O
Se(VI)
COOH
[O] = peroxides (R2O), peracids (RCOOOH), persulfuric acid...
ten Brink et al. Chem. Rev. 2004, 104, 9, 4105.
Well-Known and Widely Applied ReactionO
R OHO
R O
[O]R= alkyl or Aror
O
O
RR
O
R
[O]CHO
RR = EWD R= ED
alkaline conditions
orCOOHR
OHR
ten Brink et al. Chem. Rev. 2004, 104, 9, 4105.
Advantages:
- Compatible with several functionalities
- The regiochemistry is predictable
- Stereoselective process: migrating group retains its configuration
Exploration of the Mechanism
Renz, M.; Meunier, B. Eur. J. Org. Chem. 1999, 737.
18O-Labeled Experiment
Confirmed the presence of the Criegee intermediate
Doering, W. v.; Dorfman, E. J. Am. Chem. Soc. 1953, 75, 5595.
Retention of the Stereochemistry of the Migrating Group
Turner, R. B. J. Am. Chem. Soc. 1950, 72, 878.
Mislow, K.; Brenner, J. J. Am. Chem. Soc. 1953, 75, 2318.
based on m.p.
based on opt. rot.
Competitive Migration
O
R2R1
O
R2OR1
O
OR1R2+
O
OOH
CHCl3, 8-15 d1a-j 3a-j 4a-j
p-MeO-Ar > p-Me-Ar > Ph > p-Cl-Ar > p-Br-Ar > p-NO2-Ar
Doering, W. v. et al. J. Am. Chem. Soc. 1950, 72, 5515.
Relative Migration Aptitude
3) The peroxy acid used may have a large effect on the results obtained.
1) The ketonic substituent that can best stabilize a partial positive charge usually migrates preferentially.
2) Effect of steric demand must be kept in mind.
R RR R R
R Me
Faster migration
Slowermigration
4) These relative migratory aptitudes will be respected only if a proper stereoelectronic alignment is obtained in the Criegee intermediate. This alignment is governed by...
The primary and the secondary effect.
Krow, G. R. Org. React. 1993, 43, 251.
The Primary and Secondary Effect
Primary effect: ... antiperiplanar to the O-O bond leaving group to have the best overlap between the C-C orbital and the * O-O orbital.
Secondary effect: ... antiperiplanar to a lone pair of the hydroxyl group.
The migrating group Rm needs to be...
- Even if R is the most electron-rich group, Rm will migrate because it is properly aligned.
The Secondary Effect
OR
O
O
O
'
CF3CO3H OR
O O
O
OR
O O
OO O
+
1 2 2'
Noyori, R.; Kobayashi, H.; Sato, T. Tetrahedron Lett. 1980, 21, 2573.
when R is bulky
OR
O O
OOCOCF3HO
O
R
OO OOCOCF3
HO
The Secondary Effect
OR
O O
'
Noyori, R.; Kobayashi, H.; Sato, T. Tetrahedron Lett. 1980, 21, 2573.
oH
O
HO
R
O O
'o
H
O
HO
R
O O
'o
HO
HO
R
O O
'o
H
O
H
OCOCF3 OCOCF3 F3COCO F3COCO
3a 3b 3a' 3b'
OR
O O
OO
2
OR
O O
OO
2'
H H
When R = n-C5H11 the ratio 22' is 25: 75
Rm Rr
oH
OOCOCF3
forbiddensymmetry
The Primary Effect
According to the migratory aptitudes
Crudden, C. M. et al. Angew. Chem. Int. Ed. 2000, 39, 16, 2851.
The Primary Effect
Violation of the accepted migratory aptitudes
Crudden, C. M. et al. Angew. Chem. Int. Ed. 2000, 39, 16, 2851.
Is the Dipole/Dipole Interaction the Primary Factor? Since dipole moments are known to be stabilized by polar solvents, a decrease in selectivity would be expected as the solvent polarity increases.
O
FtBu mCPBA O O+
O O
6 7
F
F
tBu tBu
Crudden, C. M. et al. Angew. Chem. Int. Ed. 2000, 39, 16, 2851.
Is the Dipole/Dipole Interaction the Primary Factor?
Crudden, C. M. et al. Angew. Chem. Int. Ed. 2000, 39, 16, 2851.
The Rate-Determining Step of the BV oxidation
XO
mCPBAX
HOOOCOAr X O
O
***
Addition Migration
Palmer, B.W. et al. J. Am. Chem. Soc. 1970, 92, 2580.
The rate-determining step changes from addition to migration with a change of substituents.
Electrophilic and Nucleophilic Activation of the BV reaction.
O
RmR
Mn+
O
RmR
OO
H
Mn+
HB-
(1) (3)
(2)
OO-Mn+
(4)
H
O O
H
Mn+
(5)
(1) Electrophilic activation of the substrate. (H+ or Lewis Acid)
(2) Electrophilic activation of intermediate. (H+ or Lewis Acid)
(3) Nucleophilic activation of intermediate. ( base = bicarbonate)
(4) Nucleophilic activation of hydrogen peroxide. ( metal peroxo complexes)
(5) Electrophilic activation of hydrogen peroxide. (BF3)
ten Brink et al. Chem. Rev. 2004, 104, 9, 4105.
Outline
1. Introduction
2. BV mechanistic studies
3. Enantioselective reactions
3.1 Seminal work by Strukul and Bolm
3.2 Katsuki's systems
3.2.1 Bidentate ligands
3.2.2 Multidentate salen ligands
Seminal Work on Enantioselective BV O
R
n
(R-binap)Pt(2-van) (0.1 mol%)H2O2 35% ( 0.5 equiv) O
O
RH
O
n
+HR
n
Entry n R Temp. Time (min) Yield (%) ee (%)
12
3
4
5
6
7
8
9
10
2
1
1
1
Me
Me
t-Bu
n-pentyl
025
50
0
25
50
50
0
25
50
1561 18 45 (S)1223 30 37
104 28 31
1213 6 16
1288 9 14
1176 10 4
2805 2 12
4305 8 58
1284 11 50
3999 30 22
Gusso, A.; Strukul, G.et al. Organometallics 1994, 13, 3442.
Proposed Mechanism for the Enantioselective BV
R
HO
PtOH
Pt*L
*L
L*
L*
OHPt
*L
*L
+
1/2+ +
OHOPt
O*L
*LO
O
R
OOHPt
*L
*L
+
O
OOHPt
*L
*L
+
O
H2O2 +O R
R
R+
Kinetic Resolution:
Gusso, A.; Strukul, G.et al. Organometallics 1994, 13, 3442.
L*=PPH2
PPH2
Bolm's Enantioselective System
O
R
n
O2, R'CHO (0.5 equiv)CuL*2 (1mol%)
O
R
n
+O
O
Rn
L* =NO2
N
O
OH
tBuMukaiyama's process, safer and easier:
O
R' H
O2
[Ni]
O
R' OO
H
in-situ
Bolm, C. et al. Angew. Chem. Int. Ed. Engl. 1994, 33, 18, 1848.
Mukaiyama, T. et al. Chem. Lett. 1991, 641.
benzene, r.t., 20h
Bolm's Enantioselective System
Bolm, C. et al. Angew. Chem. Int. Ed. Engl. 1994, 33, 18, 1848.
Entry R'CHO R n Yield (%) ee (%)
1
2
3
4
5
6
7
8
1Ph
4-Cl-Ph 1
14-MeO-Ph
0Ph
tBuCHO
tBuCHO
tBuCHO
tBuCHO
3-Cl-PhCHO
4-MeO-PhCHO
iBuCHO
PhCHO
41 65
32
-- --
49
65 59
61 61
43 60
53 65
21 47
O
R
n
O2, R'CHO (0.5 equiv)CuL*2 (1mol%)
O
R
n
+O
O
Rbenzene, r.t., 20h
Bolm's Optimized Results
Bolm, C. et al. Synlett 2004, 9, 1619.
Ph OOH
CHP =
Katsuki's Biography
1988 University of Kyushu, Professor
1980 University of Stanford & MIT, Post-doctoral fellow Prof. K. B. Sharpless 1976 University of Kyushu, Ph.D. Prof. M. Yamaguchi
1969 University of Kyushu, B.Sc.
Tsutomu Katsuki
Proposed Enantioselective BV System
bulky R'
high conformationalfreedom
selectiveaddition
selective migration
Katsuki, T. et al. Helv. Chim. Acta. 2002, 85, 3078.
A metal complex bearing two vacant cis-coordinating sites should be suitable for asymmetric B-V reaction.
Screening Palladium(II) Complexes With Bidentate Ligands
Katsuki, T. et al. Synlett 2003, 5, 643.
OPh O
O
Ph
AgSbF6 or AgBF4 (10 mol%)UHP ( 1.3 equiv)PdCl2 2PhCN (5 mol%)L* ( 5.5 mol%)
1,2-dichloroethane, r.t.1a : 100%, 47% ee
*
Optimization of Solvent and Temp
OPh O
O
Ph
AgSbF6 or AgBF4 (10 mol%)UHP ( 1.3 equiv)PdCl2 2PhCN (5 mol%)1a ( 5.5 mol%) *
UHP=O
NH
H2NH O
OH
Katsuki, T. et al. Synlett 2003, 5, 643.
Few Substrates Tried
OR O
O
R
AgSbF6 or AgBF4 (10 mol%)UHP ( 1.3 equiv)PdCl2 2PhCN (5 mol%)1a ( 5.5 mol%) *
THF, -60 °C
Katsuki, T. et al. Synlett 2003, 5, 643.
Square Planar Complexes
Katsuki, T. et al. Tet. Lett. 2001, 41, 6911.
Square planar complex with trans vacant coordinating sites
Obtaining Vicinal Vacant Coordinating Sites
Che, C.-M. et al. J. Chem. Soc. Dalton Trans. 1997, 3479.
cis- [Mn(III) L1(acac)]
Enantioselectivity with cis- Complex
Katsuki, T. et al. Tet. Lett. 2001, 41, 6911.
- The control of the chelate conformation is not sufficient
Forced cis- Structure via a Zr Complex
activespecies
slow opening
Katsuki, T. et al. Tetrahedron Lett. 2001, 42, 3873.
Fixed conformationof the moiety
Results Obtained With Zr Complexes
Entry Catalyst Yield (%) ee (%) Config
1
2
3
4
7
8
9
10
20
68
13
12
23
87
9
1
S
R
S
-
Katsuki, T. et al. Tetrahedron Lett. 2002, 43, 4481.
Optimization of Reaction Conditions
Katsuki, T. et al. Tetrahedron Lett. 2002, 43, 4481.
Formation of Normal and Abnormal Lactones
O OO O
O
ent-ALNL21%, 88%ee 31%, 97%ee
PhCl, r.t.
cat (8 mol%)UHP (1.2 equiv) +
stopped at 54% conversion
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
O O
O
O
O
O
OO
O
Ofast-reacting isomer (16.8%)
slow-reacting isomer (29.4%)
AL : 97% ee
NL : 88% ee
+
+
ent-NL (1.3%) NL (19.7%)
ent-AL (30.6%) AL (0.5%)
Relative Reaction Ratio of EnantiomersO
O
OO O
O
ent-ALNL21%, 88%ee 31%, 97%ee
PhCl, r.t.
cat (8 mol%)UHP (1.2 equiv) +
stopped at 54% conversion
fast-reacting
slow-reacting
27% ee
krel = kfast
kslow
= ln [ (1- C) (1- ee) ]ln [ (1- C) (1+ ee) ]
Kagan 's equation
krel = = 2.0 ln [ (1- 0.54) (1- 0.27) ]ln [ (1- 0.54) (1+ 0.27) ]
C = conversion of the starting ketone
ee = ee of the unreacted ketone
Kagan, H. B.; Fiaud, J. C. Top. Stereochem. 1988, 18, 249.
Increasing Conversions
O OO O
O
ent-ALNLPhCl, r.t.
cat (8 mol%)UHP (1.2 equiv) +
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
Screening Substrates
O
ent-ALNLPhCl, r.t.
cat (8 mol%)UHP (1.2 equiv) +
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
nn n
OOO
O
OO
O
O
O O
NL: 27%, 93% eeAL: 44%, 95% ee
NL: 23%, 91% eeAL: 38%, 96% ee
NL: 55%, 80% eeAL: 25%, 99% ee
NL: 14%, 76% eeAL: 54%, 94% ee
NL: 35%, 87% eeAL: 47%, 99% ee
NL: 57%, 76% eeAL: 39%, 98% ee
Conformation Study of the Catalyst
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
N N
O OZr
Y
Y
(R)
PhPh
Y= -OPh
(R)
A
Conformation Study of the Catalyst
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
napht
N N
O OZr
Y
Y
Y= -OPh
napht
OH2
N N
O OZr
O
YOH2
A
B
HaHaHbHb
OHN N
O OZr
O
O
C
Active cis- species
Ha = 8.53 ppmHb = 3.42 ppm
Ha = 8.52 ppmHb = 3.42 ppm
Ha = 8.45 & 8.58 ppmHb = 3.90 & 4.40 ppm
Conformation Study of the Catalyst
Katsuki, T.et al. Proc. Natl. Acad. Sci. USA 2004, 101, 5737.
napht
N N
O OZrY
Y
Y= -OPh
OH2
N N
O OZr
O
YOH2
A
B
OHN N
O OZr
O
OC
OHHO
20 1
A
napht
Conclusions
- Now, great ee's can be obtained with the BV reaction
- The scope of the enantioselective BV is mainly limited to cyclobutanones
- If only one product is wanted (NL or AL) low yields are obtained since it is a kinetic resolution.
n O
O
94-99% ee
ORO
O
R *
O
O
R *Yield < 50%