Porous aromatic frameworks containing binaphthyl-dihydroazepine units (cBAPAFs) as catalytic supports for asymmetric reactions

Abstract

We present the successfully synthesis of a series of chiral polymeric aromatic frameworks containing novel enantiopure atropoisomeric 1,1′-binaphthyl-dihydroazepine-based compounds as structural building units named cBAPAFs. Three porous materials with amino, pyridinic and amino-alcohol functionalities were successfully obtained from dibrominated monomers by Suzuki-Miyaura couplings. New porous materials present surface areas up to 619 m2 g−1 determined by Brunauer–Emmett–Teller (BET), and high thermal stability. The use of nitrogen-based structural units provides useful functional groups to allow a robust binding site for metal complexes. Thus, after post-synthetic metalation with Cu(OAc)2, these materials have been applied as efficient heterogenized catalysts for the nitroaldol (Henry) reaction and a multicomponent reaction, affording chiral products with comparable enantioselectivity to that of the homogeneous system. The materials were also tested as organocatalysts for the asymmetric addition of diethylzinc to benzaldehyde and the reaction between nitro-styrene and nitroethane. These cBAPAFs could be recycled for the asymmetric nitroaldol reaction for at least 5 cycles without a significant loss in its catalytic efficiency.