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