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

The enantioselective addition of trimethylsilyl cyanide to a variety of aldehydes proceeded by the aid of a catalyst prepared in situ from titanium 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 aid of the Schiff base to the titanium alkoxide mediated silylcyanation of aldehydes. This catalyst also promoted the highly enantioselective reaction of diketene with aldehydes to give the optically active 5-hydroxy-3-oxoesters, which can be easily converted to 6-substituted-4-hydroxy lactones. These lactones are known to be a very important component of inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A(HMG-CoA) reductase such as compacitn and mevinolin. The chemical structure of chiral Schiff base-titanium alkoxide complexes is discussed based on their C-13 NMR spectra, field desorption (FD) mass spectra, and molecular weights.