One-Pot Synthesis of Polysubstituted Indoles via the Indium-Promoted Regioselective Hydrohydrazination of Terminal Alkynes

Abstract

We demonstrated that indium bromide, a trivalent indium compound with strong tolerance toward various coordination functional groups, can be used as a sole promotor to effectively promote the hydrohydrazination of a variety of N-phenylhydrazines with aromatic/aliphatic alkynes and the subsequent [3,3]-sigmatropic reaction of the hydrazone intermediate, leading to the one-pot preparation of various poly-substituted indole derivatives. Notably, the initial hydrohydrazination proceeded in a Markovnikov-type manner and showed high regioselectivity, with the hydrohydrazination of arylalkynes affording only 2-arylindole derivatives. Therefore, our findings provide a facile and practical one-pot process for the synthesis of polysubstituted indole derivatives from various phenylhydrazines and aromatic/aliphatic alkynes using only one promotor.