Lewis Acid-Catalyzed (n + 2) (n = 5, 6) High-Order Dipolar Annulation of Photogenerated Ketenes: Unified Synthesis of Seven- and Eight-Membered Diazaheterocycles.

Herein, we report a unified strategy to synthesize two series of medicinally relevant seven- and eight-membered diazaheterocycles through a Lewis acid-catalyzed (n + 2) (n = 5, 6) high-order dipolar annulation of imidazolidines and hexahydropyrimidines with in situ generated ketenes from visible-light-promoted Wolff rearrangement of α-diazoketones. This method combines operational simplicity with mild conditions, high efficiency, and broad functional group tolerance. Mechanistic investigations revealed a Lewis acid-catalyzed activation mode of ketenes. The synthetic utility was further demonstrated through gram-scale synthesis and product transformations.