Mengyu Gao, Chuanyang Song, Xintao Liu, Jingjing Zhao, Pan Li
A visible-light photocatalytic cyclopropanation of diverse alkenes using acceptor-acceptor diazoalkanes has been developed. The protocol provides an efficient and practical approach to donor-acceptor cyclopropanes under mild conditions. Experimental evidence confirms a mechanism involving a highly electrophilic triplet acceptor-acceptor carbene intermediate, followed by ultrafast intersystem crossing and ring closure.