Synthesis of 2,3‐Disubstituted Indoles from α‐Diketones and N‐Substituted Anilines

What is it about?

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.

Featured Image

Why is it important?

we report a new straightforward catalytic synthesis of 2,3-disubstituted indoles by the reaction of a-diketones and Nsubstituted anilines under reductive conditions by using a palladium phosphine catalytic system, in the absence of an external oxidant.