Synthesis of novel 2,5-dihydro- and 2,3,4,5-tetrahydro-1,2,4-triazin-5-ones from 2-arylhydrazonoacetamides and orthoesters

Reactions of 2-arylhydrazonoacetamides 1 with orthoesters were shown to give, depending on the structure of the hydrazone and the reaction conditions, either 2,3,4,5-tetrahydro-1,2,4-triazin-5-ones 2 or 2,5-dihydro-1,2,4-triazin-5-ones 3, which are very susceptible to hydrolysis to form 2-arylhydrazono-N-acylacetamides 4.