Sulfonation of pyrene-based metal–organic framework for the encapsulation of chiral organocatalyst and application in asymmetric aldol addition

Abstract

Encapsulation of bulky chiral chiral organocatalysts into metal-organic frameworks (MOFs) is a challenge because of difficult control on the crystallinity of MOFs. Herein, Zr6(μ3-OH)8(OH)8TBAPy)2 (NU-1000) with is sulfonated at − 30 °C by ClSO3H at low concentration, and then bulky cinchona alkaloid-derived chiral primary amines, 9-amino (9-deoxy)epi-quinine (QNNH2) and 9-amino(9-deoxy) epi-cinchonidine (CDNH2), are anchored to NU-1000 via acid-base reaction. At a molar ratio of QNNH2/-SO3H = 0.96, NU-1000-supported QNNH2 with high surface area (677 m2 g−1), large pore volume (0.48 cc g−1), and most probable pore size of 3.0 nm shows high yields (86–95 %) with good to excellent diasteroselectivities (anti/syn = 81/19–93/3) and enantioselectivies (89–96 %ee) in the asymmetric aldol reaction of cyclohexanone with benzaldehydes bearing electron-withdrawing groups (-NO2 and -CN) at o, m, p-positions. This work develops an effective strategy for anchoring bulky chiral organocatalyst into the porous framework of MOFs, broadening the application of MOFs in heterogeneous asymmetric organocatalysis.