Domino Electrocyclization/Azide-Capture/Schmidt Rearrangement of Dienones:  One-Step Synthesis of Dihydropyridones from Simple Building Blocks

Simple 1,4-dien-3-ones undergo Lewis acid-catalyzed Nazarov electrocyclization and intermolecular trapping by various azides to furnish 3,4-dihydropyridin-2-ones in moderate to good yields. The reaction is proposed to proceed via nucleophilic trapping of the 2-oxidocyclopentenyl intermediate, followed by Schmidt-type rearrangement to give a transient 1,4-dipole. In unsymmetrical examples, complete regioselectivity in favor of attack on the less substituted side was observed. The 1,4-dipole intermediate then rearranges to the observed dihydropyridone, via either proton transfer or 1,5-hydride shift.