Methylation of 1,2,3-thiadiazole 5-oximes and 5-N-phenylhydrazones

Abstract

1,2,3-Thiadiazoles unsubstituted at the 4-position and bearing an oxime or phenylhydrazone function at the 5-position have been prepared and treated with Meerwein's reagent. In all cases studied, preferential methylation occurs at N-3 yielding the mesoionic compounds 9 and 12. The parent oxime 6a also furnishes the N-2 methylated product 8a in substantial amounts. In contrast, when the methylation of oxime 6a is carried out with diazomethane or with methyl iodide, the nitrone 10a and the oxime ether 11a are formed. The isomeric structures of the reaction products were distinguished by their ¹³C NMR and mass spectra.