Synthesis of a phenylazo-derivative of a 1,2,3-thiadiazolium methylide. C-13/N-15 NMR characterization and crystal structure analysis

The N-phenylhydrazone derived from 4-methoxycarbonyl-1,2,3-thiadiazole-5-carbaldehyde 6 is methylated at the N-3 position, yielding the mesoionic compound 8 . The C-13 and N-15 nmr data, as well as the results from a crystal structure analysis, indicate that the molecule is best represented by the resonance forms 8A and 8B . Comparison is made with the previously synthesized thiadiazole derivative 2 which possesses thiapentalene characteristics.