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

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.