Hollow organic polymeric nano-bowls-supported BINOL-derived chiral phosphoric acid: enhanced catalytic performances in the enantioselective allylation of aromatic aldehydes

Abstract

To improve the catalytic efficiency of expensive and versatile 1, 1′-binaphthol-derived chiral phosphoric acid with 2, 4, 6-tris(isopropyl)phenyl substituents and mass transfer of reactants in heterogeneous catalysis, a hollow organic polymeric nano-bowl was used as an effective catalyst support to anchor chiral phosphoric acid through the copolymerization of vinylated 1, 1′-binaphthol with 2, 4, 6-tris(isopropyl)phenyl substituents with styrene on the surface of polystyrene nanosphere core, etching polystyrene nanosphere by DMF and then phosphorylation by POCl3. From the comparative kinetic investigation on the reaction rate of reactant in the asymmetric allylboration of 4-chlorobenzaldehyde with allylboronic pinacol ester, the as-fabricated hollow organic polymeric nano-bowl-supported chiral phosphoric acid displayed higher catalytic rates than ever-reported similar catalyst and possessed a constant catalytic rate (0.031 mol L−1 h−1) during the whole process. The expanded scope of aromatic aldehydes further proved that the hollow organic polymeric nano-bowl-supported chiral phosphoric acid was more highly active and enantioselective owing to its thin shell thickness (18 nm) and hollow structure. Due to the constant phosphorus content and well-shaped morphology of the 6th-reused catalyst, the yield of (R)-1-phenylbut-3-en-1-ol (95%) with a slightly lowered enantioselectivity (94% ee) remained constant in the sixth run. Moreover, the lowered enantioselectivity of the 6th-reused catalyst could be restored by hydrochloric acid to achieve its original enantioselectivity (96% ee), and the prothetic hollow organic polymeric nano-bowl-supported chiral phosphoric acid could effectively promote the asymmetric allylboration reaction in high yields (92–95%) with excellent enantioselectivities (94–96% ee) for another six cycles.