9-Amino(9-deoxy)epi-cinchona alkaloid-tethered aluminium phosphonate architectures for heterogeneous cooperative catalysis: asymmetric aldol and double-Michael cascade reaction

Abstract

Novel aluminium phosphonate-supported organocatalysts performing the cooperative catalysis of enamine-acid and enamine/iminium-acid were easily prepared by means of the direct and rapid precipitation of 9-amino(9-deoxy)epi-cinchona alkaloid-derived phosphonate with sodium aluminate. The heterogeneous cooperative organocatalysts with multiple functionality efficiently promoted the green aqueous asymmetric aldol addition of cyclohexanone to o, m, p-substituted benzaldehydes bearing electron-withdrawing substituents (65–98% yield, anti/syn=82:18–95:5 and 92–98%ee anti) and double-Michael of α, β-unsaturated ketones to aromatic nitroalkenes (36–85% yield, trans/cis=86:14–97:3 and 78–96%ee trans). These catalysts could be quantitatively recovered from reaction mixture by centrifugation and reused without significant loss of catalytic performances for aldol addition in the tenth run (95%, anti/syn=91:9 and 92%ee anti) and double-Michael cascade reaction in the fifth run (62%, trans/syn=89:11 and 87%ee trans). Furthermore, the arm length (n) and H+ exchange capacity resulted from POH defects had significant effects on the cooperative catalysis of 9-amino(9-deoxy)epi-cinchona alkaloid and Brønsted acid.