Asymmetric hydrogenation of unprotected indoles using iridium complexes derived from P–OP ligands and (reusable) Brønsted acids

Abstract

Unprotected indoles have been efficiently converted to enantiomerically enriched indolines (up to 91% ee) by a stepwise process: (reusable) Brønsted acid-mediated CC isomerisation and asymmetric hydrogenation using enantioselective iridium catalysts derived from P–OP ligands. This straightforward combination of (reusable) Brønsted acids, which activate the indole ring for hydrogenation by breaking its aromaticity, and enantiomerically pure [Ir(P–OP)]⁺ complexes as hydrogenation catalysts affords the resulting indolines with high enantioselectivities.