Organoboranes for synthesis. 18. C2‐symmetric α,α′‐disubstituted‐2,6‐pyridinedimethanols as catalytic chiral ligands for the enantioselective nucleophilic addition of diethylzinc to aldehydes

Abstract

Several new chiral auxiliaries with differing steric and electronic environments, such as α,α′-dimethyl-2,6-pyridinedimethanol, α,α′-ditrifluoromethyl-2,6-pyridinedimethanol, α,α′-dipentafluoroethyl-2,6-pyridinedimethanol, and α,α′-diallyl-2,6-pyridinedimethanol, have been examined and compared with α,α′-di-t-butyl-2,6-pyridinedimethanol for their ability to control the enantioselective addition of diethylzinc to benzaldehyde. The best chiral ligand has been tested for other representative aldehydes with varying steric and electronic requirements. The product alcohols are obtained in 21–78% ee. Chirality 9:506–511, 1997. © 1997 Wiley-Liss, Inc.