NEW 1,3,4-THIADIAZOLIUM-3-(UNSUBSTITUTED) METHANIDE 1,3-DIPOLES (AZOLIUM 1,3-DIPOLES) - USEFUL SYNTHONS AT -60-DEGREES-C - A NEW RING INTERCONVERSION ROUTE TO 1,2,3-TRISUBSTITUTED AND 1,2,3,4-TETRASUBSTITUTED ([1-(VINYLTHIO)-1-PHENYLMETHYLIDENE]AMINO)PYRROLES

1,3,4-Thiadiazolium-3-(unsubstituted) methanides have been trapped wit h substituted alkyne dipolarophiles at -60 degrees C giving high yield s of 2,3-di- and 2,3,4-tri-substituted ([1-(vinylthio)-1-phenylmethyli dene]amino)pyrroles from a cycloaddition rearrangement sequence. The c onformation of these molecules results in an unusual proton shielding effect in the H-1 NMR spectra. An X-ray crystal structure is reported for methyl ethylideneamino)-2-phenyl-1H-pyrrole-3-carboxylate 7a.