Synthesis of 2,3‐Disubstituted Indoles from α‐Diketones and N‐Substituted Anilines: One‐Pot Pd‐Catalyzed Reductive Amination

Herein, we report a new straightforward catalytic synthesis of 2,3-disubstituted indoles from α-diketones 1 and N-substituted anilines 2 by employing a palladium(II) trifluoroacetate/1,1′-bis(diphenylphosphino)ferrocene ([Pd(tfa)2]/dppf; 1:1.5) under reductive conditions and without an external oxidant. The tandem reaction involves ketoenamine and ketoamine as intermediates and a final dehydration–annulation reaction to obtain the 2,3-disubstituted indole. New palladium hydride species, which catalyze the reaction, could not be isolated but Pd–H species were observed by NMR and IR spectroscopy and mass spectrometry (FAB+) studies. This work presents a new regioselective route with a plausible mechanism to synthesize 2,3-disubstituted indoles under reductive conditions.