a new multicomponent reaction catalyzed by [lewis acid] [co(co)4
TRANSCRIPT
A New Multicomponent Reaction Catalyzed by[Lewis acid]+[Co(CO)4]- Catalyst
T. L. Church, C. M. Byrne, E. B. Lobkovsky, andG. W. CoatesJACS ASAP
DOI: 10.1021/ja069065d
Current Literature - June 16, 2007
Maciej Walczak @ Wipf Group 1 6/20/2007
Multimetallic Catalysis
- Majority of the catalytic systems arebased on catalytic-stoichiometricsystems (NHK coupling).
- Although sequential addition of metalcatalyst has been successfully applied,there are only few well-defined,multimetallic (multifuntional) catalyticsystems (Sonogashira coupling,Wacker oxidation).
- Ideally, multimetallic catalyst(heteronuclear) would be superior to amixture of salts.
Maciej Walczak @ Wipf Group 2 6/20/2007
Epoxide Carbonylation
- Detailed mechanistic studies showed thatreaction rate is independent on epoxide andCO, but 1st order in catalyst.
- The rate is strongly dependent on thepolarity of the solvent.
- Rate determining step is lactone formation.
- Solvents with a strong donating capabilitieshelp to stabilize aluminum cation formedafter lactone formation.
Coates
J. Am. Chem. Soc. 2006,, 128, 10125
NN
O OAl
O
Ot-But-Bu
t-But-Bu [Co(CO)4]-1 =
Maciej Walczak @ Wipf Group 3 6/20/2007
Epoxide Carbonylation
Coates J. Am. Chem. Soc. 2002, 124, 1174Coates Angew. Chem. Int. Ed. 2002, 41, 2781Coates J. Am. Chem. Soc. 2005, 127, 11426
- A practical procedure for carbonylation of epoxides has been also developed (1 atm CO, yields>98%).
Coates Org. Lett. 2006, 8, 3709
O
R+ CO
NN
N NCr
Et
Et
EtEt
Et
Et
EtEtR
THF
THF
Co(CO)4-
+
O
R
O
>88%
R = various alkyl groups
NN
O OAl
O
Ot-But-Bu
t-But-Bu [Co(CO)4]-
O
R+ CO
O
R
O
60-90%or Cp2Ti(THF)2
+ [Co(CO)4]-
Maciej Walczak @ Wipf Group 4 6/20/2007
Carbonylation of 4-membered Heterocycles
NN
O OAl
O
Ot-But-Bu
t-But-Bu [Co(CO)4]-1 =
X
R1 R2
+ COCatalyst X
R1 R2
O
Maciej Walczak @ Wipf Group 5 6/20/2007
Synthesis of Anhydrides
Inversion of configuration is consistentwith mechanism involvingnucleophilic displacement by CO.
Coates J. Am. Chem. Soc. 2004, 126, 6842
OO
R R1
OO
RR1
O
Catalyst (0.33 - 5 mol%)200 psi, PhMe, 24 h
yields: 90-99%R = H, MeR1 = only alkyl
+ CO
OO
Me
OO
Me
O
Cat., 55 o
200 psi, PhMe, 24 h+ CO
99% ee 99% ee
OO
Me
O
88% ee
Cat., 80 o
200 psi, PhMe, 24 h
However, partial racemization was observed when the reaction was carried out at elevatedtemperatures (80 o).
O
Me+ CO
NN
N NAl
R1
R1
R
R1
R1 R R1
R1
R
R1R1
R
THF
THF
Co(CO)4-
+
R = 4-ClC6H4
R1 = H
OO
O
97%
Direct insertion into epoxides:Coates Chem. Comm. 2006, 657
Maciej Walczak @ Wipf Group 6 6/20/2007
Insertion into Nitrogen Heterocycles
N
R3 R2
R1
N NO O
R3R3R2
R2
R1R1
CO
60 atm
+ +
N I
Cat.
Entry R1 R2 R3 Cat. Mol% N I
1 B n H M e A 5 9 0 ND
2 B n H M e B 5 5 0 ND
3 B n -(CH2)4- A 5 8 0 ND
4 B n -(CH2)4- B 5 < 5 ND
5 B n -(CH2)4- Co2(CO)8 8 2 8 ND
6 To s H M e A 5 3 5 ND
7 To s H M e B 5 9 9 ND
8 B n M e CH2OTB S A 5 9 0 5
9 B n M e CH2OTB S Co2(CO)8 8 9 2 8
Coates Angew. Chem. Int. Ed. 2002, 41, 2781
Other heterocycles, such as azirines, α-lactams, diaziridines, azetidines and oxazilines havebeen described.
N
OAr
N
O
Ar
O
+ CO 13 atm
5 mol% Co
60 oC, 24 h, THF
variable yield9-92%
Maciej Walczak @ Wipf Group 7 6/20/2007
Title Paper - Experiment Design
Maciej Walczak @ Wipf Group 8 6/20/2007
Title Paper - Optimization Studies
Maciej Walczak @ Wipf Group 9 6/20/2007
Title Paper - Reaction Scope
Maciej Walczak @ Wipf Group 10 6/20/2007
Lewis Acids Promote Acyl Migration
Maciej Walczak @ Wipf Group 11 6/20/2007
Summary and Outlook
• Lewis acids combined with nucleophilic metal carbonyls are powerful catalyst forcarbonylations of epoxides and aziridines.
• Detailed mechanistic studies allowed for development of efficient multicomponentreactions using epoxides, CO, and isocyanates.
Future Directions:Reaction scope needs to be improved - since CO is an invariable component,other electrophilic acceptors may be used.
Although some efforts were directed towards development of enantioselectiveversion of the epoxide carbonylation, more research is needed to develop optimalconditions for kinetic resolution.
A concept of Lewis acid activation followed by trapping by nucleophilic metalcenters could be potentially extended towards other substrates.
Maciej Walczak @ Wipf Group 12 6/20/2007