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

• Published in: Tetrahedron: asymmetry Vol. 12; no. 5; pp. 755 - 760
• Main Authors: Lake, Fredrik, Moberg, Christina
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 02.04.2001
• Subjects: aliphatic-aldehydes; bis(sulfonamido) bis(amide) complexes; catalytic enantioselective addition; crystal-structures; dialkylzinc reagents; disulfonamide-ti(o-iso-pr)4-dialkyl zinc system; disulfonamides; exchange-reaction; functionalized secondary alcohols; tetradentate ligand
• ISSN: 0957-4166; 1362-511X; 1362-511X
• DOI: 10.1016/S0957-4166(01)00111-2

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 (1 R,2 R)-1,2-diphenyl-1,2-ethanediamine and (1 S,2 S)-1,2-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 (1 R,2 R)-1,2-diphenyl-1,2-ethanediamine only (i.e. without the chiral sulfonamide), the ( S)-product formed with a 3% e.e. The effects of 24 chiral additives on the Ti-mediated addition of diethylzinc to benzaldehyde were examined in the presence of 4; e.e.s of the products ranged from 26% for the ( R)-enantiomer to 72% for the ( S)-enantiomer.