Confinement-Driven Enantioselectivity in 3D Porous Chiral Covalent Organic Frameworks.

Abstract

3D covalent organic frameworks (COFs) with well-defined porous channels are shown to be capable of inducing chiral molecular catalysts from non-enantioselective to highly enantioselective in catalyzing organic transformations. By condensations of a tetrahedral tetraamine and two linear dialdehydes derived from enantiopure 1,1'-binaphthol (BINOL), two chiral 3D COFs with a 9-fold or 11-fold interpenetrated diamondoid framework are prepared. Enhanced Brønsted acidity was observed for the chiral BINOL units that are uniformly distributed within the tubular channels compared to the non-immobilized acids. This facilitates the Brønsted acid catalysis of cyclocondensation of aldehydes and anthranilamides to produce 2,3-dihydroquinazolinones. DFT calculations show the COF catalyst provides preferential secondary interactions between the substrate and framework to induce enantioselectivities that are not achievable in homogeneous systems.