Catalyst-free chemoselective conjugate addition and reduction of α,β-unsaturated carbonyl compounds via a controllable boration/protodeboronation cascade pathway

A novel, efficient transition-metal-free and controllable boration/protodeboronation strategy has been developed for the chemoselective conjugate addition and 1,4-reduction of alpha,beta-unsaturated carbonyl compounds. Without any metal-catalyst or base, a series of beta-boration products of alpha,beta-unsaturated carbonyl compounds was easily obtained in moderate to excellent yields in a mixed solvent of ethanol and water. The presence of a catalytic amount of Cs2CO3 can effectively induce further protodeboronation reaction towards 1,4-reduction products at higher reaction temperature. Therefore, by slightly changing the reaction conditions, the boration or reduction products of alpha,beta-unsaturated carbonyl compounds can be controllably obtained. Mechanistic studies revealed that Cs2CO3 played the key role in activating the protodeboronation step. This transition-metal-catalyst-free and product controllable method provides a useful and eco-friendly tool for the highly chemoselective preparation of the beta-boration products and 1,4-reduction products of alpha,beta-unsaturated carbonyl compounds.