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

Chemoselective reductions of alpha,beta-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-alpha,beta-unsaturated cycloketones and acyclic alpha,beta-unsaturated ketones in the presence of H3N center dot BH3 under catalyst-free conditions. The polarized H3N center dot BH3 preferred to coordinate with the polarized C=O 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.

Automated summary

In this study, a catalyst-free and efficient method using H3N•BH3 for the chemoselective reduction of α,β-unsaturated cycloketones and acyclic α,β-unsaturated ketones is described. The method is expedient, green, and applicable.