Synthesis of 9-nitro-5H-spiro[benzo[b]tetrazolo[1,5-d][1,4]oxazepine-4,2′-oxirane] via an unusual ring-expansion

Attempted cyclization of (4-(hydroxymethyl)-8-nitro-4H-benzob]tetrazolo1,5-d]1,4]oxazin-4-yl)methyl 4-methylbenzenesulfonate 2 did not give the expected spirooxetane product 1, but instead provided 9-nitro-5H-spirobenzob]tetrazolo1,5-d]1,4]oxazepine-4,2′-oxirane] 3via an unusual ring-expansion process. The structure of compound 3 was confirmed by single-crystal X-ray crystallography. The spiroepoxide (oxirane) in compound 3 could be ring-opened with a variety of nucleophiles to give products of potential interest to medicinal chemists.