Intramolecular azide trapping of the Nazarov intermediate: formation of peroxy-bridged indolizidinones via a deep-seated rearrangement and aerobic oxidation.

Cross-conjugated dienones with pendent azide side chains undergo interrupted Nazarov trapping, leading to peroxy-bridged indolizidinones in good yields. This process is proposed to involve skeletal rearrangement of the initial trapping product, with loss of dinitrogen, to give an intermediate 1,4-betaine, which then undergoes reaction with atmospheric oxygen. The endoperoxide products can be reduced under catalytic hydrogenation conditions to furnish alpha-hydroxylactams. [reaction: see text].