Chemoselective reduction of α,β-unsaturated ketones to allylic alcohols under catalyst-free conditions

Abstract

Chemoselective reductions of α,β-unsaturated ketones to afford the corresponding allylic alcohols have always been challenging. Precious metals and ligands have always been employed in these transformations. Herein, we describe an ever more expedient, green and general method for the chemoselective reductions of exo- and endo-α,β-unsaturated cycloketones and acyclic α,β-unsaturated ketones in the presence of H₃N·BH₃ under catalyst-free conditions. The polarized H₃N·BH₃ preferred to coordinate with the polarized CO bond, forming a six-membered transition state, and then the reduced products were furnished via a concerted double hydrogen transfer process. This well explained the absolute chemoselectivity.