New ring-transformation reaction: the conversion of a tetrazole ring into a 1-oxa-3,4-diazine ring

New ring cleavage/ring closure reactions of tetrazole derivatives provide a route to a new heterocyclic system such as furazano[3,4-e]-1-oxa-3,4-diazine, which was characterized by ¹H, ¹³C and ¹⁴N NMR spectroscopy and X-ray crystallography.