Chiral Bimetallic Catalysts Derived from Chiral Metal Phosphates: Enantioselective Three-Component Asymmetric Aza-Diels-Alder Reactions of Cyclic Ketones

摘要

A new type of chiral bimetallic catalyst is disclosed. These chiral bimetallic catalysts are easily formed through mixing a metal Lewis acid and a metal binaphthyl phosphate (MLA/M[P](3)) in solution. H-1 and P-31 NMR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and X-ray crystallographic analysis reveal a bimetallic structure of the Y(Yb)(III)/Y[P](3) complexes with bridging binaphthyl phosphate ligands. The Lewis acidity of these chiral bimetallic catalysts is readily tuned by changing either the metal Lewis acid or the chiral metal phosphate. Through cooperative metal Lewis acid-enamine catalysis, asymmetric three-component aza-Diels-Alder reactions of 5-, 6-, and 7-membered cyclic ketones, unsaturated ketoesters, and arylamines were successfully achieved to afford fused bicyclic dihydropyridines in high yields (up to 94%) with high enantioselectivity (up to 99% enantiomeric excess) and excellent chemoselectivity.