Regioretention Probes Distinguish Ring Scission Mechanisms in Nitrogen Insertion Reactions

Atom insertion reactions into ring systems may occur via one of two pathways, proceeding either through initial cyclization to form a 3-membered ring intermediate followed by cleavage of the ring-fusion bond, or through initial ring-scission followed by recyclization onto the inserting atom. Herein, we demonstrate the use of regioretention probes, substrates with latent symmetry that is unveiled only in the case of ring scission and are thus able to distinguish between possible mechanisms for atom insertion. We apply these probes to a handful of previously reported nitrogen insertion methods and in each case unambiguously establish whether the reaction proceeds through aziridination or C=C cleavage. In particular, we show that recently reported cobalt- or manganese-catalyzed nitrogen insertion protocols, postulated to proceed via an aziridinyl radical intermediate, instead proceed through a ring-opened ketone-containing intermediate.