Dehydrogenative Aromatic Ring Fusion for Carbazole Synthesis via C-C/C-N Bond Formation and Alkyl Migration

An intermolecular dehydrogenative annulation (IDA) for carbazole synthesis via sequential C–C/C–N bond formation with a selective alkyl group migration is reported. Using the hypervalent iodine(III) reagent PhI(OAc)2 (PIDA), in a one-pot operation, up to five C(sp2)–H bonds, one N(sp3)–H bond functionalization, and one alkyl (Me, Et) group migration could all be achieved from non-prefunctionalized 1,3,5-trialkylbenzenes and anilides under ambient laboratory conditions. Mechanistically, it is shown that PIDA reacts with anilides to generate a nitrenium ion or an equivalent carbenium ion which influences the second aromatic ring to be activated for C–C/C–N bond formation. Strategically, regioselective fusion of arenes to anilides is described.