The Stetter Reaction, Benzoin Condensation, and Pinacol Coupling

The Stetter Reaction, Benzoin Condensation, and Pinacol Coupling [Pg.31]

Virtually, all reports in this reaction class exploit catalysis by NHCs. [Pg.31]

A highly enantioselective synthesis of a-amino acid derivatives employs an NHC-catalysed intermolecular Stetter reaction of an o, /3-unsaturated ester with an aldehyde. The key steps of (i) C-C bond formation between Breslow intermediate 0 and Michael acceptor and (ii) asymmetric protonation are efficiently combined, giving ees of 85-99%. [Pg.31]

Enals (92) react with modified chalcones (e.g. 93) in an enantioselective Stetter reaction, giving highly functionalized products (94) in ees up to 97%, using chiral NHC catalysis. A Michael-type addition of NHC-bound enal acyl anion to the chalcone is proposed. [Pg.31]

The mechanism of the enantioselective intramolecular Stetter reaction, catalysed by a chiral azolium-NHC, has been investigated for tlie example of salicylaldehyde derivative (95) to give /3-ketoester (96). Kinetics are first order in both aldehyde and catalyst, and the aldehydic proton exhibits a primary kinetic isotope effect. Transfer [Pg.31]