Asymmetric Anisoin Synthesis Involving Benzoin Condensation Followed by Deracemization

The highly enantioselective synthesis of p-anisoin was achieved via the benzoin condensation of a prochiral p-anisaldehyde using achiral NHC catalysts such as vitamin B1. In this reaction, p-anisoin crystallized as a conglomerate, and the deracemization of racemic p-anisoin under basic conditions was efficiently performed by Viedma ripening. Although the handedness of the enantioselective crystallization could not be controlled by spontaneous crystallization, it could be controlled by the coexistence of a catalytic amount of optically active valine. It was clarified that this is due to the asymmetric transformation of p-anisoin with enantiomeric valine in the mother liquor.