Formyl- and Acyl-1,2,3-Triazoles

In the still more 7t-deficient 1,2,3-triazole series (see 20), several 4-amino-5-formyl derivatives resisted both direct acylation and acetal formation. A successful alternative was to form intermediates with side chains conjugated to the nucleus. For example, 1- and 2-methyl-, as well as 3-benzyl-4-amino-l,2,3-triazole-5-aldehydes reacted with a cold mixture of dimethylformamide and phosphoryl chloride to give excellent yields of, e.g., 3-benzyl-4-dimethyl-aminomethyleneamino-l,2,3-triazole-5-aldehyde (84). This was converted to 9-benzyl-8-azapurine (see 21) in excellent yield by refluxing in methanolic ammonium acetate.87 In a variation of this reaction, an imidate (85) replaced the amidine (84) as intermediate. Thus, 4-amino-l-methyl-l,2,3-triazole-5-aldehyde and triethyl orthoacetate, refluxed for 2 hr, gave an excellent yield of 4-ethoxyethylideneamino-l,2,3-triazole-5-aldehyde (85), cyclized, by stirring in cold ethanolic ammonia, to 2,7-dimethyl-8-azapurine (good yield).87... 

The preparation and reactions of the azine, phenylhydrazone, and phenyl-semicarbazone of 4-amino-5-formyl-2-methyltriazole proceeded normally. One acetal has been prepared as follows. 4-Amino-3-benzyl-5-formyltriazole and boron trifluoride (as diethyl ether complex), stirred in methanol, gave 4-amino-3-benzyl-5-dimethoxymethyltriazole (20°C, 6 hr, 53%) and a dimeric by-product, 4-amino-3-benzyl-5-(3-benzyl-5-dimethoxytriazol-4-ylimino-methyl)triazole [73JCS(P1)2037]. The amino group in 4-aminotriazole-5-carbaldehydes lends itself readily to the formation of amidines and imidates (Section III,B,1), but it resists acylation. 

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