Cobalt(II)‐based Metalloradical Activation of 2‐(Diazomethyl)pyridines for Radical Transannulation and Cyclopropanation

A new catalytic method for the denitrogenative transannulation/cyclopropanation of in‐situ‐generated 2‐(diazomethyl)pyridines is described using a cobalt‐catalyzed radical‐activation mechanism. The method takes advantage of the inherent properties of a CoIII‐carbene radical intermediate and is the first report of denitrogenative transannulation/cyclopropanation by a radical‐activation mechanism, which is supported by various control experiments. The synthetic benefits of the metalloradical approach are showcased with a short total synthesis of (±)‐monomorine. Denitrogenative transannulation/cyclopropanation of in‐situ‐generated 2‐(diazomethyl)pyridine is presented, which involves a cobalt‐catalyzed radical‐activation mechanism. A cobalt(II)‐metalloradical undergoes radical addition to alkynes during denitrogenative transannulation, or to alkenes during cyclopropanation, forming indolizines and cyclopropanes, respectively