Difluorocarbene Generation\nvia a Spin-Forbidden Excitation\nunder Visible Light Irradiation

The\ngeneration of difluorocarbene from difluoromethane\nbis(sulfonium\nylide) <b>1</b> through spin-forbidden excitation under irradiation\nwith 450 nm blue light was reported. The formation of difluorocarbene\nwas confirmed by its reaction with styrene derivatives for the generation\nof difluorocyclopropanation and insertion into RX–H bonds (X\n= O, S) for the generation of RXCF<sub>2</sub>H. The spin-forbidden\nexcitation mechanism for the formation of difluorocarbene from difluoromethane\nbis(sulfonium ylide) was supported by spectroscopic and kinetic studies\nas well as computational chemistry. The homolytic cleavage of two\nS–C bonds in compound <b>1</b> under irradiation was\nconfirmed by time-resolved EPR spectroscopic studies of the precursor’s\nfree-radical-capturing reaction, as well as the isolation of the dimer\nof dimethyl (phenylthiol)malonyl radical. Further studies showed that\nthe homolytic cleavage process occurred asynchronously in the solvent\ncage based on the isotope-labeled scrambling experiments and DFT calculations.