Catalytic Asymmetric ”Aldol" Reaction

Significance

Hayashi and co-workers describe a direct asymmetric organocatalytic self-aldol reaction of acetaldehyde. The reaction consumes three equivalents of acetaldehyde to afford the ­acetal 2 with an enantiomeric ratio of 91:9. For er determination and isolation, the authors found it necessary to derivatize the diastereomeric mixture 2 to butane-1,3-dibenzoate 3, which was obtained in an overall yield of 56%. Two further synthetic transformations which do not compromise the acetal’s enantiomeric excess are reported. The reaction is thought to proceed via enamine catalysis.