Magnesium(II)-catalyzed asymmetric hetero-Diels-Alder reaction of Brassard's dienes with isatins

The first catalytic asymmetric hetero-Diels-Alder reaction of Brassard's dienes with isatins was realized using Mg(II)/N,N'-dioxide complexes as catalysts, affording the corresponding chiral spirolactones bearing tetrasubstituted centers in up to 99% yield with up to 99% ee and >99:1 dr within 3 hours. In the mechanism, based on the operando IR experiments, a predominant Diels-Alder pathway was found in the reaction. A possible transition state model was also proposed.