Synthesis and Properties of 3,6-Diamino-substituted 1,2,4-Triazin-5(2H)-ones

The ultrasound-promoted cyclocondensation of N(1)-amino-N(2)-arylmethyl- (or aryl-) guanidines 2 with ethyl 2-amino-2-thioxoacetate furnished novel 3,6-diamino-substituted 1,2,4-triazin-5(2H)-ones 4 in moderate to high yields. The acylation of compounds 4 occurred regioselectively at ring position 2, presumably favoured by the formation of an intramolecular hydrogen bond. In accordance with this assumption, the acetylation of 6-amino-3-[benzyl(methyl)amino]-1,2,4-triazin-5(2H)-one (9) did not afford the 2-acetyl derivate 11 but rather the 6-acetamido derivative 10.