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 α,β-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.