Photochemical deracemization of α-chiral carboxamides mediated by inter- and intramolecular hydrogen bonding.

Photochemical deracemization allows for the direct generation of enantiomerically pure or enriched compounds from their racemates employing a single chiral catalyst. In the present study, carboxylic acid amides (carboxamides) with a substituent in the α-position were investigated in a photochemical deracemization mediated by a chiral aromatic ketone. The catalyst displays a hydrogen bonding site which allows for a differentiation between the two enantiomers and operates by a reversible hydrogen atom transfer. It was found that α-alkoxy or α-amino substituents enable an efficient deracemization (up to 99.5 : 0.5 e.r.) due to a second intramolecular hydrogen bonding interaction locking a distinct substrate conformation.