Aromatization and ring cyclization: A reasonable understanding on the ring cyclization mechanism of 3-amino-6-hydrazino-1,2,4-triazin-5(2H)-one reacted with one-carbon fragment reagents or nitrous acid

✍ Scribed by Long-Chih Hwang; Chun-Hsien Tus; Jung-Hui Wang

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2006
• Tongue: English
• Weight: 347 KB
• Volume: 43
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570430412

✦ Synopsis

Abstract

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The cyclization mechanism for the title compound (2) reacting with one‐carbon fragment reagents or nitrous acid to afford heterobicyclic compounds 6‐amino‐3‐substituted‐1,2,4‐triazolo[3,4‐f][1,2,4]triazin‐8(7__H__)‐ones (3a∼d) or 6‐amino‐1,2,3,4‐tetrazolo[5,1‐f][1,2,4]triazin‐8(7__H__)‐one (4), respectively, is explored in this paper. When 3‐amino‐2‐benzyl‐6‐hydrazino‐1,2,4‐triazin‐5(2__H__)‐one (10), the N‐2 benzylated derivative of 2, is treated under the same conditions, ring cyclization does not occur; instead, 3‐amino‐2‐benzyl‐6‐substituted‐1,2,4‐triazin‐5(2__H__)‐ones (11,12,14) and 2‐N‐(2‐amino‐1‐benzyl‐4‐oxo‐1,2,4‐triazin‐5‐yl)semicarbazide (13) are formed. Alternatively, when 3‐amino‐6‐hydrazino‐2‐[(2‐hydroxyethoxy)methyl]‐1,2,4‐triazin‐5(2__H__)‐one (16), a compound bearing the 2‐[(2‐hydroxyethoxy)methyl] side‐chain at N‐2 of 2 by an NCO bond, reacts with glacial acetic acid or nitrous acid, the side‐chain is cleaved through acidolysis to affford the ring‐closed compound 6‐amino‐3‐methyl‐1,2,4‐triazolo[3,4‐f][1,2,4]triazin‐8(7__H__)‐one (3b) or compound 4, respectively. From these results, we suggest a cyclization mechanism that the ring cyclization is dependent on the aromatization of the 1,2,4‐triazine ring, which influence the reactivity and reaction behavior of the π‐deficient 1,2,4‐triazine.