The boron effect on radical difluoromethylation of N-sulfonyl cyclic ketimines

Abstract

The intermediary-produced difluoromethyl radical, produced by one-electron oxidation of difluoromethylborates [pinB(Aryl)CF₂H][K(18-cr-6)] (pinB = 4,4,5,5-tetramethyl-1,3,2λ²-dioxaborolane) using photo-redox catalysts (PCs), is advantageous for converting N-sulfonyl cyclic ketimines to the corresponding difluoromethylated benzene-fused γ-sultams. Several mechanistic studies indicated the considerable interaction between the difluoromethyl radical and aryl boronate (Ar-Bpin), which would promote the difluoromethylation of the cyclic imine unit. The particular (catalytic) effect of Ar-Bpin was qualitatively supported by characterizing the facilitation of the PC-mediated difluoromethylation with sodium difluoromethanesulfinate (HCF₂SO₂Na).