ASYMMETRIC CARBON-CARBON BOND-FORMING REA CTIONS 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 ga ve 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 aldeh ydes. This catalyst also promoted the highly enantioselective reaction of diketene with aldehydes to give the optically active 5-hydroxy-3-o xoesters, which can be easily converted to 6-substituted-4-hydroxy lac tones. These lactones are known to be a very important component of in hibitors of 3-hydroxy-3-methylglutaryl coenzyme A(HMG-CoA) reductase s uch as compacitn and mevinolin. The chemical structure of chiral Schif f base-titanium alkoxide complexes is discussed based on their C-13 NM R spectra, field desorption (FD) mass spectra, and molecular weights.