Synthesis of 1H-1,2,4-triazole 2-oxides and annelated derivatives

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Abstract
SS-Dimethylsulphimides (1)–(4) have been prepared from N-arylbenzamidines, 2-aminopyridines, 2-aminopyrazine, and 2-aminopyrimidines. The sulphimides react with nitrile oxides at room temperature or below to give the 1H-1,2,4-triazole 2-oxides (5) and the annelated derivatives (6)–(8). The structures of the 1,2,4-triazolo[1,5-a]pyridine 3-oxides (6a, d, e, and h) are established by an independent synthesis involving the oxidation by lead tetra-acetate of the amidoximes (9a–d). The N-oxides are readily deoxygenated by reaction with phosphorus trichloride; in addition the N-oxides (6d and e) are deoxygenated by heating under reflux in toluene, oxygen being transferred to the solvent. The reversible ring-opening of 5,7-dimethyl-2-(4-tolyl)-s-triazolo[1,5-a]pyrimidine (8c) is detected by n.m.r. spectroscopy.

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