Studies on the copper hydride mediated reductive aldol addition via enolborates & its applications

Abstract

A reductive aldol addition via enolborates has been developed. α,β-Unsaturated ketones, esters and amides are used as substrates, reduced by in situ generated copper hydride, from Cu(OAc)2.H2O, phosphine ligand, and with pinacolborane (PinBH) as the stoichiometric reductant. The enolborates thus generated reacted with aromatic, unsaturated, and aliphatic aldehydes to give syn-aldol adducts as the major product with good to excellent yields (up to 98 %) and good syn-diastereoselectivity (up to d.r > 20 : 1). Even for the more challenging substrates such as cyclic, β-monosubstituted or β,β-disubstituted Michael acceptors, synthetically useful aldol products were obtained.