The first 1,4,2-Oxathiazolium salts: Remarkable similarities to their 1,3,4-isomers

5-Methylmercapto-1,4,2-oxathiazoles, formed by 1,3-dipolar cyclo-addition between nitrile oxides and methyl dithiocarboxylates, are readily solvolysed with strong acid and an acyl anhydride to give in high yields the first examples of 1,4,2-oxathiazolium salts. Remarkable similarities between the C-13 NMR spectra of these and identically-substituted 1,3,4-oxathiazolium salts suggest that electronically the structures of the isomeric cations are very close.