Abstract
The catalytic asymmetric α-benzylation of aldehydes represents a highly valuable reaction for organic synthesis. For example, the generated α-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 α-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 Brønsted and Lewis acidic sites, robust chiral confinement space, and visible-light induced photothermal conversion. These features allow it to highly promote the intermolecular asymmetric α-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 α-benzylation reactions on various substituted aldehydes and alkyl bromides.
Highlights
The catalytic asymmetric a-benzylation of aldehydes, rst reported by List and coworkers, has been recognized as a very valuable reaction for organic synthesis,[1] and the generated aheteroarylmethyl aldehydes are an important class of intermediates to access pharmaceuticals and natural products
For achieving a-benzylation of aldehydes in a facile, sourceand energy-saving way, we report a chiral BINOLphosphate ((R)-BINOLPA-DA) and Cu(II)-porphyrin (Cu(II)TAPP) derived multifunctional chiral covalent framework (CCOF) by imine-condensation
With (R)-CuTAPBP-covalent organic frameworks (COFs) in hand, we examined its asymmetric catalytic activity based on the model reaction of propionaldehyde with 4-(bromomethyl)pyridine to form (R)MPP, a synthon to angiogenesis inhibitors
Summary
The catalytic asymmetric a-benzylation of aldehydes, rst reported by List and coworkers, has been recognized as a very valuable reaction for organic synthesis,[1] and the generated aheteroarylmethyl aldehydes are an important class of intermediates to access pharmaceuticals and natural products. Upon visible-light irradiation, the obtained (R)-CuTAPBP-COF exhibits excellent catalytic activity and enantioselectivity toward intermolecular a-benzylation of aldehydes with less sterically hindered alkyl halides via photothermal conversion (Scheme 1).
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