Aromatization and ring cyclization: A better understanding on the ring cyclization mechanism of 3-amino-6-hydrazino-1,2,4-triazin-5(2H)-one reacted with acetic acid in N,N-dimethylformamide

✍ Scribed by Long-Chih Hwang; Rang-Rong Wu; Chun-Hsien Tu

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2005
• Tongue: English
• Weight: 121 KB
• Volume: 42
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570420516

✦ Synopsis

Abstract

In this paper we report that the title compound (3) reacts with excess N,N‐dimethylformamide (DMF) containing two equivalents of acetic acid to afford 6‐amino‐1,2,4‐triazolo[3,4‐f][1,2,4]triazin‐8(7__H__)‐one (1). When 3‐amino‐2‐benzyl‐6‐hydrazino‐1,2,4‐triazin‐5(2__H__)‐one (6), the N‐2 benzylated derivative of 3, is treated under the same conditions, ring cyclization does not occur; instead, 3‐amino‐2‐benzyl‐6‐(2‐formyl‐hydrazino)‐1,2,4‐triazin‐5(2__H__)‐one (7) is formed. Single‐crystal X‐ray analysis of a 3‐ethyl derivative of compound 1 reveals the predominant tautomeric structure to be the 7__H__‐tautomer (7__H__‐1). From these results, we propose a reasonable cyclization mechanism that incorporates two important points: (1) the tautomerism of the N‐2 hydrogen with the C‐5 oxo group aromatizes the 1,2,4‐triazine ring, and (2) the DMF is proto‐nated by acetic acid on the nitrogen atom, then deamination occurs where DMF is attacked by the 6‐hydrazino group of 3 or 6.