N-Heterocyclic carbene-catalyzed [4 + 2] annulation of α,β-unsaturated carboxylic acids: enantioselective synthesis of dihydropyridinones and spirocyclic oxindolodihydropyridinones

The N-heterocyclic carbene-catalyzed generation of dienoate from alpha,beta-unsaturated carboxylic acid via the in situ formed mixed anhydride, and the following [4 + 2] annulation with hydrazones and isatin-derived imines was developed, affording the corresponding dihydropyridinones and spirocyclic oxindolodihydropyridinones, respectively, in moderate to good yields with good to excellent enantioselectivities.