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.