α,α-Difluorinated Allylsulfones: <i>gem</i>-Difluoroethylenyl Reagents for Synthesis of Fluorinated Chiral α-Quaternary Amino Acids

Among numerous fluorine-containing molecules, chiral <i>gem</i>-difluoroethylenes (C═CF₂) exhibited unique properties in agrochemicals, pharmaceuticals, and materials science. However, the general synthetic methods were limited to the functionalization/defluorination of trifluoromethylalkenes. Here, we disclose a new type of difluoroethylenyl reagent, α,α-difluoro allylsulfones, which allows highly enantioselective Cu-catalyzed desulfonylative S_N2' substitution with benzylideneamino esters. This protocol presents a novel strategy for the construction of diversified chiral α-quaternary amino acid derivatives containing a <i>gem</i>-difluoroethylene moiety with excellent results (up to 86% yield, generally 90-98% ee). The ease of synthesis of α,α-difluoro allylsulfones, synthetic applications of this protocol, and transformations of products revealed the potential utility of this chemistry.