Chiral 3,3′-diaroyl BINOL phosphoric acids: Syntheses, photophysical, electrochemical studies and their utility in asymmetric catalysis

Abstract

An efficient synthesis of the enantiomerically pure 3,3′-diaroyl BINOLs is accomplished through chemoselective Weinreb ketone synthesis from Weinreb amide derivative of chiral BINOL-3,3ʹ-dicarboxylic acid using Grignard reagent. This protocol facilitated the introduction of the aroyl group at the 3,3′-position on the 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 yield 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.