Asymmetric α-Arylation of Aldehydes

Significance

The first amine-catalyzed enantio­selective α-arylation of aldehydes is reported. These products are assumed to be formed via the Michael reaction of an aldehyde 2 derived enamine intermediate with a quinone 1 and subsequent proton transfers (aromatization). Aldehydes 3 are in equilibrium with hemiacetals 4 which could be isolated as single diastereomers. In order to obtain good conversions of the starting materials, the presence of an excess of water was crucial, due to its possible involvement in the proton-transfer reactions. Furthermore, the authors presented transformations of hemiacetals 4 leading to optically active quinones and to doubly acetylated products without loss of enantiopurity.