Visible-light-mediated cyclopropanation reactions of 3-diazooxindoles with olefins

Visible-light-mediated metal-free cyclopropanation reaction of diazo compounds with different olefins or arenes have been fully developed in recent years. However, electron-deficient olefins still could not be well tolerated in these reactions. Here, by using 3-diazooxindole as the carbene precursor, the visible-light-mediated cyclopropanation reaction of diazo compounds with electron-deficient olefins was successfully developed. The electron-rich olefins were also well tolerated in the reactions. A series of spirocyclopropyloxindoles were synthesized in moderate to high yields under mild, metal-free conditions. Mechanism studies reveal that both singlet and triplet carbenes are probably involved in the reaction.