1,2,3-Thiadiazol-3-ium-3-methanide (ylide) 1,3-dipoles: cycloaddition-rearrangement sequences leading to substituted 1-(2-vinylthioethenyl)pyrazole systems: azolium 1,3-dipoles

Alkylation of 4,5-dialyl-1,2,3-thiadiazoles and 1,2,3-benzothiadiazoles wit h trimethylsilylmethyl trifluoromethanesulfonate occurred at N-3. Treatment of the salts with CsF generated new 1,2,3-thiadiazol-3-ium-3-methanide 1,3 -dipoles. These gave in situ cycloaddition-rearrangement reactions with som e alkyne and alkene dipolarophiles leading to new substituted 1-(2-vinylthi oethenyl)pyrazole systems, where a second molecule of dipolarophile was add ed at the thiol SH which was generated by opening of the thiadiazole ring. H-1, C-13 and N-15 NMR spectra are reported, as well as X-ray crystal struc tures on dimethyl 1-{(Z)-2-[(Z)-1,2-bis(methoxycarbonyl)-vinylthio]-1,2-dip henylethenyl}-1H-pyrazole-3,4-dicarboxylate 6a and 1-[(Z)-2-cyanoethylthio- 1,2-diphenylethenyl]-4,5-dihydro-1 H-pyrazole-3-carbonitrile 10. The X-ray data on 6a suggested a weak chalcogen effect from the pyrazole 2-N to the n earby S-atom.