Ligand Control of Diastereodivergency in Asymmetric Inverse Electron Demand Diels–Alder Reaction

A diastereodivergent direct catalytic
asymmetric inverse electron
demand Diels–Alder reaction between ketenes and 3-alkylenyloxindoles
was accomplished by using chiral N,N′-dioxide/gadolinium complexes. By adjusting only the substituents
of the ligand and retaining other catalysis conditions, both syn- and anti-indole-fused dihydropyranones
bearing two vicinal stereogenic centers were obtained in high yields
with excellent ee values. Thus, by changing the configuration of the
chiral ligands, all stereoisomers could be obtained from the same
set of starting materials.