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

Unprotected indoles have been efficiently converted to enantiomerically enriched indolines (up to 91% ee) by a stepwise process: (reusable) Bronsted acid-mediated C=C isomerisation and asymmetric hydrogenation using enantioselective iridium catalysts derived from P-OP ligands. This straightforward combination of (reusable) Bronsted 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.