ASYMMETRIC CARBON-CARBON BOND-FORMING REACTIONS CATALYZED BY CHIRAL SCHIFF BASE-TITANIUM ALKOXIDE COMPLEXES

The enantioselective addition of trimethylsilyl cyanide to a variety o f aldehydes proceeded by the aid of a catalyst prepared in situ from t itanium tetraisopropoxide [Ti(O-i-Pr)(4)] and chiral Schiff bases and gave the corresponding cyanohydrins in high optical yield (up to 96% e .e.). A remarkable rate enhancement was brought about by the addition of the Schiff base to the titanium alkoxide mediated silylcyanation of aldehydes. This catalyst system also promoted the highly enantioselec tive reaction of diketene with aldehydes, which led to the formation o f optically active 5-hydroxy-3-oxoesters.