Reactions of 4-amino-5-(4,6-dimethyl-2-pyrimidinyl)-2,3-dihydro-1,2,4-triazole-3-thione with C-electrophiles

The title 1,2,4-triazole-3-thione 2 reacted, with ethyl bromoacetate in ethanol in the presence of sodium ethoxide to form, S-alkyl derivative 3 and its cyclocondensation product - 3-(4,6-dimethyl-2pyrimidinyl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-6(5H)-one (4), whereas with 4-chloroacetoacetate under similar conditions only corresponding cyclocondensation product 5a was isolated. Reaction of 2 with (omega-bromoacetophenone gave 6-hydroxy-3-(4,6-dimethyl-2-pyrimidinyl)-6,7-dihydro-6-phenyl-5H-[1,2,4]triazolol[3,4-b][1,3,4]thiadiazinium bromide (6), which under treatment with sodium hydroxide was converted into corresponding 1,3,4-thiadiazine 5b Heating 2 with ethyl orthoformate or 4-chlorobenzaldehyde afforded 4-(methylidene)amino substituted derivatives 7a,b. Condensation of 2 with benzoic acid in phosphorus oxychloride gave 3-(4,6 dimethyl-2-pyrimidinyl)-6-phenyl-[1,2,4-triazolo][3,4-b][1,3,4]thiadiazole (8). Reaction of 2 with acetic anhydride yielded triacetylderivative 9.