Hemin-Catalyzed Oxidative Phenol-Hydrazone [3+3] Cycloaddition Enables Rapid Construction of 1,3,4-Oxadiazines

Herein, we present
a hemin-catalyzed oxidative phenol-hydrazone [3+3] cycloaddition that
accommodates a broad spectrum of N-arylhydrazones,
a class of less exploited 1,3-dipoles due to their significant Lewis
basicity and weak tendency to undergo 1,2-prototropy to form azomethine
imines. It renders expedient assembly of diversely functionalized
1,3,4-oxadiazines with excellent atom and step economy. Preliminary
mechanistic studies point to the involvement of a one-electron oxidation
pathway, which likely differs from the base-promoted aerobic oxidative
scenario.