Chiral 3,3′-diaroyl BINOL phosphoric acids: syntheses and evaluation in asymmetric transfer hydrogenation, photophysical, and electrochemical studies

Abstract

An efficient synthesis of enantiomerically pure 3,3′-diaroyl BINOLs is accomplished through chemoselective Weinreb ketone synthesis from the Weinreb amide derivative of chiral BINOL-3,3′-dicarboxylic acid using a Grignard reagent. This protocol facilitated the introduction of the aroyl group at the 3,3′-position of binaphthol. The 3,3′-diaroyl BINOL phosphoric acid has been prepared and evaluated for asymmetric transfer hydrogenation of 2-aryl/alkyl quinolines. The 3,3′-diaroyl BINOL phosphoric acids are found to be efficient catalysts in the hydrogenation of 2-aryl quinolines using Hantzsch ester to generate 2-aryl tetrahydroquinolines in excellent yields with moderate enantioselectivity. The presence of aroyl units, a photosensitizer core, in 3,3′-diaroyl BINOL prompted us to evaluate their photophysical and electrochemical properties, as these molecules may be a potential candidate for asymmetric photocatalysis.