Desulfonylative Coupling of Alkylsulfones with gem-Difluoroalkenes by Visible-Light Photoredox Catalysis

The desulfonylative radical addition of tertiary alkyl groups to gem-difluoroalkenes by photoredox Ir-catalyst is described. This method exhibits broad substrate scope, affording structurally diverse (E)-fluoroalkene derivatives in a highly stereoselective manner. The resulting (E)-fluoroalkenes were converted into complex fused cyclic compounds by intramolecular cyclization reactions. Control experiments and theoretical calculations are consistent with a single Ir catalyst playing the dual role of generating radical species from sulfones via single electron transfer and mediating Z/E isomerization via energy transfer. A subset of fluoroalkenes provided Z stereoisomers with >90% selectivity, but the same alkenes could also be obtained as E isomers with high selectivity by taking advantage of a secondary Z to E photoisomerization.