Azides, acid catalyzed ring rearrangement

Dihydropyridones 110 are prepared from l,4-dien-3-ones 105 by a combination of electrocyclization with Schmidt reaction. Thus, enone 105 undergoes Lewis acid-catalyzed Nazarov electrocyclization, the resulting Nazarov intermediate 106 is trapped with benzyl azide, and ring expansion of the resulting azide 107 delivers zwitterion 108. This intermediate rearranges to the dihydropyridone 110 via either proton transfer or 1,5-hydride shift. 

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