Mesoionic compounds derived from pyrazole, isothiazole, and isoxazole

Abstract

A number of novel mesoionic compounds related to dehydrodithizone (2,3-diphenyltetrazolium 5-sulphide) have been obtained by deprotonation of 2-methyl-4-methyl-(or 4-p-tolyl-)sulphonylamino-pyrazolium, -isothiazolium and -isoxazolium perchlorates. The pyrazoliumsulphonamidates (9b) and (9c) rearrange to covalent aminopyrazoles on thermolysis; a similar methyl migration occurs when 1,2-dimethyl-3,5-diphenylpyrazolium 4-oxide is heated. Attempted cycloaddition of the pyrazoliumsulphonamidates to dimethyl acetylenedicarboxylate resulted in the loss of an N-methyl group and formation of pyrazolylfumaric esters. Spectroscopic experiments indicate that whereas 2-methyl-3,5-diphenylisoxazolium 4-oxide (26) decomposes rapidly, the related 4-toluene-p-sulphonamidate (24) is stable in dilute solution.