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Mechanistic Insights on Cooperative Asymmetric Multicatalysis Using Chiral Counterions

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Title Mechanistic Insights on Cooperative Asymmetric Multicatalysis Using Chiral Counterions
 
Creator JINDAL, G
SUNOJ, RB
 
Subject COUNTERANION-DIRECTED CATALYSIS
TRANSITION-METAL CATALYSIS
ATTRACTIVE NONCOVALENT INTERACTIONS
CENTER-DOT-O
C-H
DENSITY FUNCTIONALS
PALLADIUM CATALYSIS
ALLYLIC ALKYLATIONS
PHOSPHORIC-ACIDS
ALPHA-ALLYLATION
 
Description Cooperative multicatalytic methods are steadily gaining popularity in asymmetric catalysis. The use of chiral Bronsted acids such as phosphoric acids in conjunction with a range of transition metals has been proven to be effective in asymmetric synthesis. However, the lack of molecular-level understanding and the accompanying ambiguity on the role of the chiral species in stereoinduction continues to remain an unresolved puzzle. Herein, we intend to disclose some novel transition state models obtained through DFT(B3LYP and M06) computations for a quintessential reaction in this family, namely, palladium-catalyzed asymmetric Tsuji-Trost allylation of aldehydes. The aldehyde is activated as an enamine by the action of a secondary amine (organocatalysis), which then adds to an activated Pd-allylic species (transition metal catalysis) generated through the protonation of allyic alcohol by chiral BINOL-phosphoric acid (Bronsted acid catalysis). We aim to decipher the nature of chiral BINOL-phosphates and their role in creating a quaternary chiral carbon atom in this triple catalytic system. The study reports the first transition state model capable of rationalizing chiral counterion-induced enantioselectivity. It is found that the chiral phosphate acts as a counterion in the stereocontrolling event rather than the conventional ligand mode.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-12-29T05:46:26Z
2014-12-29T05:46:26Z
2014
 
Type Article
 
Identifier JOURNAL OF ORGANIC CHEMISTRY, 79(16)7600-7606
0022-3263
http://dx.doi.org/10.1021/jo501322v
http://dspace.library.iitb.ac.in/jspui/handle/100/17229
 
Language English