Imprint of free space around acid site in hollow mesoporous polymeric solid acid and application in heterogeneous acetal hydrolysis/asymmetric aldol tandem reaction

Tailoring free spaces around catalytic sites in a controlled way is highly attractive for improving the accessibility of reactants to catalytic sites in heterogeneous catalysis. In this paper, the free space around latent acid site (-SH) in the mesoporous shell of hollow polymeric nano-bowl was constructed through the hydrolysis of attached thiuronium/Co(OH)(2) complex and the formation/removal of Co(OH)(2) porogen in the shell. After the oxidation of -SH moiety by H2O2, the as-obtained hollow mesoporous bowl-like polymeric solid acid could be conveniently functionalized by 9-amino-(9-deoxy)cinchonidine (CDNH2) via acid-base reaction to afford multifunctional nano-bowl Poly(St/SO3H) HMOBs with 0.34 mmol g(-1) of loaded CDNH2 and 1.77 mmol g(-1) of acid capacity. In heterogeneous acetal hydrolysis/asymmetric aldol tandem reaction, Poly(St/SO3H-CDNH2) HMOBs displayed moderate to excellent catalytic performances (90-95% yields, anti/syn = 81/19-95/5 and 74-97%ee anti) for the starting benzaldehyde methyl acetals bearing electron-withdrawing substituents (R = NO2, Cl) at o, m and p-positions.