Unanticipated formation of a novel octaazacyclodecane ring upon oxidation of a 1,1‐bis‐urazole

• Published in: Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2018-05, Vol.74 (5), p.558-563
• Main Authors: Breton, Gary W., Martin, Kenneth L.
• Format: Article
• Language: English
• Subjects: Bonding strength; Chemical bonds; crystal structure; Crystallography; Oxidation; persistent radicals; radical dimer; tetrahydrotetrazole; tetrazole; Tetrazoles; tetrazolidine; urazole radicals
• ISSN: 2053-2296; 0108-2701; 2053-2296; 1600-5759
• DOI: 10.1107/S2053229618005211

Tetrahydrotetrazoles are a little‐explored class of five‐membered heterocycles with four contiguous singly‐bonded N atoms. Recent work in our labs has demonstrated that urazole radicals are amenable to N—N bond formation via radical combination to form such a chain of four N atoms. Previously described 1,1‐bis‐urazole compounds appeared to be convenient precursors to the target tetrazoles via their oxidation to intermediate urazole diradicals, which upon N—N bond formation would complete the tetrazole framework. While oxidation proceeded smoothly, the novel 10‐membered octaaza heterocycle 7,7,18,18‐tetraacetyl‐4,10,15,21‐tetraphenyl‐1,2,4,6,8,10,12,13,15,17,19,21‐dodecaazapentacyclo[17.3.0.02,6.08,12.013,17]docosan‐3,5,9,11,14,16,20,22‐octone, C42H32N12O12, was obtained (36% yield) instead of the expected tetrazole product, as confirmed by X‐ray crystallography. Calculations at the (U)B3LYP/6‐311G(d,p) level of theory suggest that the desired tetrazoles have weak N—N bonds connecting the two urazole units. Tetrahydrotetrazoles are a little‐explored class of five‐membered heterocycles with four contiguous singly‐bonded N atoms. Their attempted synthesis via N—N bond formation between two suitably‐substituted urazole rings led to the unanticipated formation of a novel octaazacyclodecane ring system.