Ti-mediated addition of diethylzinc to benzaldehyde. The effect of chiral additives

In the presence of a chiral tridentate bissulfonamide, the titanium-mediated addition of diethylzinc to benzaldehyde gave alkylated products ranging from the (R)-enantiomer, formed with an e.e. of 26%, to the (S)-enantiomer, formed in 72% e.e. The enantioselectivity was also affected by the presence of additional chiral mono- and bidentate ligands, with the reactions proceeding via complexes containing the chiral sulfonamide and the additive. The: addition of (1R,2R)-2,2-diphenyl-,12-ethanediamine and (1S,2S)-1.3-diphenyl-1,2-ethanediamine gave the (S)-product with e.e. of 49% and the (R)-product with 16% e.e., respectively, whereas without additives the (R)-product was obtained in 26% e.e, In the presence of (1R,2R)-1,2-diphenyl-1,2-ethanediamine only (i.e. without the chiral sulfonamide), the (S)-product formed with a 3% e.e. (C) 2001 Elsevier Science Ltd. All rights reserved.