A general electron transfer reduction of lactones using SmI₂–H₂O

Herein we describe a strategy for the selective, electron transfer reduction of lactones of all ring sizes and topologies using SmI₂–H₂O and a Lewis base to tune the redox properties of the complex. The current protocol permits instantaneous reduction of lactones to the corresponding diols in excellent yields, under mild reaction conditions and with useful chemoselectivity. We demonstrate the broad utility of this transformation through the reduction of complex lactones and sensitive drug-like molecules. Sequential electron transfer reactions and syntheses of deuterated diols are also described.