Chiral Bis-Oxalamide-Rare Earth Complex Catalyzed Inverse- Electron-Demand Asymmetric oxa-Hetero-Diels-Alder Reaction for Optically Active Dihydropyran Core Structures

Chiral bis-oxalamide (CBOA)/rare-earth metal complexes-catalyzed asymmetric inverse-electron-demand oxa-hetero-Diels-Alder (HDA) reactions were investigated under mild reaction conditions, which was performed between beta,gamma-unsaturated alpha-ketoesters and various electron-riched dienophiles, such as cyclopentadiene, 2,3-dihydrofuran, 3,4-dihydro-2H-pyran, tetrahydropyridine as well as phenyl(vinyl)sulfane. Several series of optically active functionalized 3,4-dihydro-2H-pyran or ring fused dihydropyran derivatives were obtained in high yields with high diastereo- and enantioselectivity. The procedure was able to tolerate a relatively wide range of substrates. The coordination mode of chiral bis-oxalamide with Sc(III) was demonstrated by the X-ray crystallographic structure, and DFT calculations were carried out to uncover the regio- and stereocontrol.