Photocatalyzed [2+1] cyclization of alkenes and silylated trifluorodiazoethanes: facile entry into (difluoromethylene)cyclopropanes

Methylenecyclopropanes are among the most robust building blocks in synthetic chemistry, but the study on (difluoromethylene)-cyclopropanes is rather limited, because of the difficulty in the synthesis of these compounds. Herein, we report the invention of a novel carbene precursor, (1-diazo-2,2,2-trifluoroethyl)dimethyl(phenyl)silane ( 1a ) and its application in the synthesis of (difluoromethylene)cyclopropanes. The reaction proceeds through photocatalyzed [2+1] cyclization of readily available alkenes and diazo compound 1a followed by the work-up of the reaction through the elimination of silyl fluoride. Both aromatic and aliphatic alkenes are tolerated by the mild reaction conditions, affording various (difluoromethylene)cyclopropanes in 44%–82% yield (>30 examples). Gram scale reaction and diversified downstream transformations highlight the synthetic potential of this methodology. The experimental and DFT calculations suggest the involvement of triplet carbene intermediate.