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The azomethine nitrene. I. Pyrolysis and photolysis of Δ 2 1,2,4‐oxadiazoline‐5‐ones
Author(s) -
Boyer J. H.,
Frints P. J. A.
Publication year - 1970
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570070109
Subject(s) - chemistry , nitrene , isocyanic acid , amidine , dehydrogenation , photochemistry , cyclohexanone , photodissociation , nitrile , fragmentation (computing) , medicinal chemistry , organic chemistry , catalysis , computer science , operating system
Both photolytic and pyrolytic fragmentation of the oxadiazolone ring produces carbon dioxide and a residue which may exist in part as an intermediate azomethine nitrene and may react with or without rearrangement and/or further fragmentation. Rearrangement produces carbodiimides 2 and cyanamides 6. Thermal and photo‐isornerization of carbodiimides into cyanamides provides a key step in an explanation for the formation of the latter from an oxadiazolone. A highly selective cyclization produces a benzimidazole 3 when a suitable aryl subsliluent is at nitrogen. The formation of N ‐phenylbenzamidine 7a from 3‐phenyl‐4‐benzyloxadiazolone 5c requires a 1,4‐migration from carbon to nitrogen followed by hydrolysis. The same or similar migration of hydrogen and subsequent ring‐closure with dehydrogenation provides the formation of 2‐phenyl‐quinazoline 8. Products which require no rearrangement of the residue include amidines 7 and triazoles 10. A portion of each triazole corresponds to a nitrile, in turn a product along with a simple nitrene;, of more extensive fragmentation of the; oxadiazolone ring. Phenyl, benzyl, and cyclohexyl nitrenes are respectively detected by the isolation of aniline, benzaldehyde and cyclohexanone. Other recombination reactions bring about the formation of triphenyltriazine 13 and triphenylimidazole 14.