Synthesis of (1,2,4)triazolo(1,5-c)pyrimidine derivatives.

Abstract

Condensation of diaminomethylenehydrazones with ethoxymethylenemalononitrile (2) gave 2, 3-dihydro [1, 2, 4] triazolo [1, 5-c] pyrimidines in moderate to high yields. Of the variously substituted diaminomethylenehydrazones, amino (monosubstituted amino) methylene ones were most reactive in this condensation, regardless of the nature of the 4-substitutent. The reaction was found to be initiated at N-3 by attack on the ethoxymethine carbon of 2, followed by an electrocyclic reaction to form the bicyclic pyrimidine. The 2, 3-dihydro compounds were oxidized with iron (III) chloride in aqueous acetic acid or iodine in ethyl alcohol to give the corresponding [1, 2, 4] triazolo [1, 5-c] pyrimidines.