CHIRAL TRIALKYLBORANE REDUCING AGENTS - PREPARATION OF 1-DEUTERIO PRIMARY ALCOHOLS OF HIGH ENANTIOMERIC PURITY

B-3-Pinanyl-9-borabicyclo[3.3.1]nonane (3-pinanyl-9-BBN, prepared from (+)-α-pinene and 9-BBN) is an effective chemical reagent for the asymmetric reduction of 1-deuterio aldehydes to chiral 1-deuterio primary alcohols. For example, benzaldehyde-Z-d is reduced to pure (S)-(+)-benzyl-1-d-alcohol. A deuterated reagent prepared from a-pinene and 9-BBN-9-d was found to reduce a variety of aromatic, aliphatic, and α,β-unsaturated aldehydes to the corresponding chiral primary 1-deuterio alcohols. In each case a large excess of the R enantiomer is formed. Steric factors seem to have little effect on the extent of asymmetric induction, but electron-donating para substituents on benzaldehyde slightly decrease the enantioselectivity of the reduction. A number of other chiral-9-BBNderivatives were investigated. A model is proposed to account for the high asymmetric inductions. © 1979, American Chemical Society. All rights reserved.