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Combination of a Metal-N-Heterocyclic-Carbene Catalyst and a Chiral Aminocatalyst within a Covalent Organic Framework: a Powerful Cooperative Approach for Relay Asymmetric Catalysis.

Incorporation of metal catalysis and organocatalysis has emerged as a promising way for developing new and valuable organic reactions. This catalytic strategy would potentially enable unprecedented transformations not possible by the existing metal catalysis or organocatalysis alone. Herein, we report an imine-linked chiral covalent organic framework (CCOF) achieved by the combination of a Au-N-heterocyclic-carbene (NHC-Au) monomer with its chiral secondary amine-containing counterpart via an updated direct synthetic approach. The obtained CCOF can be used as a reusable dual catalyst to highly promote the asymmetric aryl methanol oxidation-aldol relay reaction in a heterogeneous way. In addition, the CCOF-based shaped setup was also realized via a facile templating freeze-drying approach based on an eco-friendly chitosan material, by which the gram-scale asymmetric aerobic alcohol oxidation-aldol relay reaction was successfully achieved. The potential utility of this approach is highlighted by the preparation of many more new CCOF-based multifunctional heterogeneous catalysts to promote various asymmetric organic transformations in a facile and green way, and further progress might eventually allow CCOF catalysts to be developed for industrial processes.