Preparation of 4-benzylsulfanyl[1,2,3,5]dithiadiazol-1-ylium chlorides: potential precursors to meso-ionic 1,2,3,5-dithiadiazolium-4-thiolate

Treatment of S-benzyl-iso-thiuronium chlorides with sulfur monochloride (S2Cl2) gives the corresponding S-benzyl-1,2,3,5-thiadiazolium chlorides 2 as deep red crystalline compounds. The structure of the p-chlorobenzyl derivative 2a has been confirmed by X-ray crystallography. Attempts to generate the unknown type-B meso-ionic compound 1,2,3,5-dithiadiazolium-4-thiolate 1 by reaction of these salts with nucleophiles were unsuccessful. AM1 semi-empirical molecular orbital calculations suggest that, although the meso-ionic structure corresponds to a local energy minimum, acyclic valence tautomers could equilibrate in solution and lead to further reaction