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.

Automated summary

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). The synthetic potential of this methodology is highlighted by gram scale reaction and diversified downstream transformations. Experimental and DFT calculations suggest the involvement of triplet carbene intermediate.