Regio- and enantioselective nucleophilic addition to gem-difluoroallenes

Allenes that bear three carbons connected by cumulative double bonds are useful building blocks owing to their high chemical reactivity. In particular, allenes with two geminal or 1,1-difluoro groups have attracted substantial research interest in recent decades. However, the development of catalytic methods for the stereoselective transformation of gem-difluoroallenes in a diversity-oriented fashion remains a largely unsolved problem. Here we report the highly tunable, catalytic nucleophilic addition of gem-difluoroallenes at the β- and γ-positions with thiols to access a variety of substituted difluoroethenes and difluoropropenes. By combining a rhodium catalyst with bidentate N or P ligands, the addition of S–H bonds across the difluoroallenes occurs with a high chemoselectivity, regioselectivity and enantioselectivity and with full atom economy. This chemistry extends to the catalytic enantioselective γ-addition of amine N–H bonds, which demonstrates the generality of the strategy. Computational studies reveal the origins of selectivity between β- and γ-addition, the formation of Z-isomers as major products in β-addition and the enantiocontrol with γ-addition.