Lieve Bastin

Reactions of 5-chloro-1,2,3-thiadiazolium salts with activated methylene compounds

The N-3 and N-2 methylated 1,2,3-thiadiazolium tetrafluoroborates 3 and 4 react with aliphatic activated methylene ketones and esters in the presence of a base to give the substitution products 7–11 and 18–24. Under similar conditions activated methylene azoles afford products formulated by NMR analysis as N–S ⋯ O rotamers (25, 26), N–S ⋯ N rotamers (12–15, 27–29), or a mixture of both (16, 17, 30). The X-ray crystal structure analysis of product 21, derived from the thiadiazolium salt 4 and 2,2-dimethyl-1, 3-dioxane-4, 6-dione, reveals a nearly linear N–S ⋯ O sequence (169°) and a short S ⋯ O contact (2.37/2.34 A) for the two independent molecules.

Synthesis of 6aλ4-thia-1,2,3,5,6-pentaazapentalenes

The title compounds have been obtained from 5-amino-1,2,3-thiadiazole 6 by methylation and reaction with arenediazonium tetrafluoroborates; their 13C NMR data and X-ray analysis are discussed in terms of two non-equivalent resonance contributors 11A and 11B.

Reactions of methylated 5-chloro-1,2,3-thiadiazolium salts with cyclohexane-1,3-diones: X-ray crystal structure analysis of the thiapentalenic products

The N-3 methylated thiadiazolium salt 3 reacts with cyclohexane-1,3-dione and 5,5-dimethylcyclohexane-1,3-dione to give mesoionic 1,2,3-thiadiazoles (5 and 6) with short intramolecular S ⋯ O contacts, whereas the N-2 methylated thiadiazolium salt 4 furnishes oxathiole derivatives (7 and 8) with short intramolecular S ⋯ N contacts.

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

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 Meerweins 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.