Application of metal-free conditions to a one-pot Leimgruber–Batcho indole synthesis

Abstract

A metal-free, one-pot synthesis of 2,3-unsubstituted indoles via an adapted Leimgruber–Batcho protocol has been developed. The process incorporates a chemoselective reduction of an aromatic nitro group using tetrahydroxydiboron and 4,4′-bipyridine, enabling efficient access to indole scaffolds under mild conditions. Application of this method resulted in comparable or improved yields relative to existing metal-based protocols. The successful preparation of 6-bromo-5-methoxyindole, a key constituent of breitfussin C, G, and H, shows the utility of this method for the synthesis of indoles relevant to natural product synthesis.