A 2-methylthio-3,5-diaryl-1,3,4-thiadiazolium cation; its reactions, and further exploration of the chemistry of 2-alkyl-3,5-diaryl-1,3,4-thiadiazolium cations

Activation of a representative 3,5-diaryl-1,3,4-thiadiazole-2-thione by thione S-methylation gives a cation that is readily susceptible to nucleophilic substitution. Reactions with diethyl malonate, ethyl acetoacetate, acetylacetone, cyclopentan-1,3-dione, or 3-ethylrhodanine under basic conditions lead to β,β-disubstituted methine bases and (or) β-substituted methine bases in cases where deacetylation occurs under the reaction conditions. This cation and the 2-alkyl-3,5-diaryl-1,3,4-thiadiazolium cation are convenient sources of a series of neutral and cationic dyes containing the 1,3,4-thiadiazole ring system.