Sulfoximine-titanium reagents in enantioselective trimethylsilylcyanations of aldehydes

Chiral titanium reagents derived from optically active sulfoximines and Ti(O-i-Pr)(4) promote the asymmetric addition of trimethysilyl cyanide to aldehydes affording cyanohydrins in high yields with good enantioselectivities (up to 91% ee). The ligand structure and the reaction conditions have been optimized. With substoichiometric amounts of the sulfoximine-titanium reagent the product is obtained in decreased yield with lower enantiomeric excess. The molecular structures of (R)-S-(2-hydroxyphenyl)-S-methyl sulfoximine [(R)-4a] and (R)-S-(2-hydroxyphenyl)-S-(1,1-dimethylethyl) sulfoximine [(R)-4d] have been determined by X-ray diffraction analysis.