1,6-Dihydro-1,2,4-triazines

Abstract

Synthetic pathways to reduced 1,2,4-triazines have been investigated. The most convenient route involved the reaction of ketones with sodium cyanide and thiosemicarbazide, under acidic conditions, to yield cyanothiosemi-carbazones. These compounds were either converted into the corresponding carboxy-thiosemicarbazones which, in turn, were cyclized in diphenyl ether, or they were treated with concentrated hydrochloric acid to effect ring closure directly. The alkylation of 3-thioxo-5-oxo- and 3,5-dithioxo-derivatives was examined. Studies of replacement reaction of thioxo- and methylthio-groups in the 3- and 5-positions showed that the 5-position was more active than the 3-. I.r. and n.m.r. spectra were used to assign the preferred tautomeric form of a number of the products.