Reductive Cyclopropanation through Bismuth Photocatalysis.

We present here a catalytic method based on a low-valent Bi complex capable of cyclopropanation of double bonds under blue LED irradiation. The catalysis features various unusual Bi-based organometallic steps, namely, (1) two-electron inner sphere oxidative addition of Bi(I) complex to CHI, (2) light-induced homolysis of the Bi(III)-CHI bond, (3) subsequent iodine abstraction-ring-closing, and (4) reduction of Bi(III) to Bi(I) with an external reducing agent to close the cycle. Stoichiometric organometallic experiments support the proposed mechanism. This protocol represents a unique example of a reductive photocatalytic process based on low-valent bismuth radical catalysis.