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 Co-III-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.