A BINOL-phosphoric acid and metalloporphyrin derived chiral covalent organic framework for enantioselective α-benzylation of aldehydes

The catalytic asymmetric alpha-benzylation of aldehydes represents a highly valuable reaction for organic synthesis. For example, the generated alpha-heteroarylmethyl aldehydes, such as (R)-2-methyl-3-(pyridin-4-yl)propanal ((R)-MPP), are an important class of synthons to access bioactive drugs and natural products. We report herein a new and facile synthetic approach for the asymmetric intermolecular alpha-benzylation of aldehydes with less sterically hindered alkyl halides using a multifunctional chiral covalent framework (CCOF) catalyst in a heterogeneous way. The integration of chiral BINOL-phosphoric acid and Cu(II)-porphyrin modules into a single COF framework endows the obtained (R)-CuTAPBP-COF with concomitant Bronsted and Lewis acidic sites, robust chiral confinement space, and visible-light induced photothermal conversion. These features allow it to highly promote the intermolecular asymmetric alpha-benzylation of aldehydes via visible-light induced photothermal conversion. Notably, this light-induced thermally driven reaction can effectively proceed under natural sunlight irradiation. In addition, this reaction can be easily extended to a gram-scale level, and its generality is ascertained by asymmetric alpha-benzylation reactions on various substituted aldehydes and alkyl bromides.

Automated summary

This study reports a facile approach for the asymmetric intermolecular alpha-benzylation of aldehydes using a multifunctional chiral covalent framework catalyst. The reaction can effectively proceed under natural sunlight irradiation and shows broad generality.