Highly enantioselective cyanation of aldehydes catalyzed by a multicomponent titanium complex.

A new multicomponent bifunctional catalytic system based on a titanium complex was used for the efficient enantioselective cyanation of aldehydes. The catalyst was readily prepared from tetraisopropyl titanate (Ti(Oi-Pr)4), (S)-6,6'-dibromo-1,1'-bi-2-naphthol (1e), cinchonine (2a), and (1R,2S)-(-)-N-methylephedrine (3b). It was revealed that the combination of 1e, 2a, 3b, and Ti(IV) was essential in this cyanation. The reaction proceeded smoothly in the presence of a catalytic amount of the multicomponent catalyst to afford the desired cyanohydrins ethyl carbonates in moderate to excellent isolated yields (up to 95%) with high enantioselectivities (up to 94% ee). A catalytic cycle based on experimental phenomena was proposed to explain the origin of the asymmetric induction.