1.2.4- Triazoles diacylhydrazines

Diacylhydrazines (32) on heating with a primary amine undergo cyclization to the 1,2,4-triazole derivative (38). It is assumed that the amidrazone (37) is an intermediate in the reaction. Most practical syntheses of 1,2,4-triazoles now utilize an amidrazone or a derivative of this alicyclic intermediate containing three nitrogen atoms, and these variations are discussed in Chapter 4.12. 

Reaction of 232 with 4-substituted l,3-oxazol-5(4/7)-one 247 led to diacylhydrazines 248 or to imidazole derivatives 249 depending on the reaction temperature (Scheme 24). l,2,4-Triazole-3-thione 250 was obtained by a two-step sequence from 232 with phenyl isothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 251. The effects of hydrazones 241-246 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions of Chlorella vulgaris were investigated <2005CEC622>. 

Under anhydrous conditions 3,6-diphenyl-1,4-dihydro-1,2,4,5-tetrazine isomerizes to the 4-amino-1,2,4-triazole derivative (326). Hydrolysis under the influence of acids or bases transforms the 1,4-dihydro-1,2,4,5-tetrazine system to diacylhydrazines (329), carboxylic acids (330), and hydrazine, 1,3,4-oxadiazoles (328), or 1,2,4-triazoles (327) depending on the reaction conditions <78HC(33)1077>. 

Triazoles are available via cyclodehydration reactions of At.At -diacylhydrazine with amines, although the conditions are often quite vigorous. An interesting variant utilises ijm-triazine (1,3,5-triazine) as an equivalent of HN(CHO)2. Condensations of aminoguanidine with esters give the versatile 3-amino compounds. ... 

This MCR synthesis, in principle, is related to the (earlier) formation of 3,5-disubstituted 1,2,4-triazoles 22 by cyclocondensation of 1,2-diacylhydrazines 20 with ammonia, which likewise proceeds via an amidrazone 21 acylated at the terminal hydrazone position ... 

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