An Atropisomerically Enforced Phosphoric Acid for Organocatalytic Asymmetric Reactions

Three BINOL-derived phosphoric acids exhibiting atropisomerism in the 3,3′-positions were obtained by Suzuki coupling reaction. The diastereomeric mixture was resolved by HPLC. Structural assignment was achieved by NOE-NMR analysis and by TD-DFT simulation of the electronic circular dichroism (ECD) spectra. The three atropisomeric catalysts were tested in three enantioselective reactions, comparing their ability to induce enantioselectivity with related, well-known, phosphoric acid structures. All three catalysts were competent in promoting the reactions, rendering excellent enantioselectivity (98 % ee) in one case. The atropisomeric features at the 3,3′-position were indeed found to influence the outcome of the reaction, demonstrating the potential of atropisomeric conformational control at the 3,3′-position of the BINOL core in the rationalization of catalyst performances and in the design of new efficient structures.