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