THE MECHANISM OF THE THERMOLYTIC RING-OPENING OF 5-AZIDO-4-FORMYL-3-METHYL-1-PHENYLPYRAZOLE

Thermolysis of 5-azido-4-formyl-3-methyl-1-phenylpyrazole 4 produces t he (4-cyanopyrazol-3-ylmethyl)pyrazoles 3 and 6. 2-Cyano-3-phenylazo-2 -butenal 2 was detected by H-1 NMR spectroscopy during the reaction. T he products 3 and 6 and other rearrangement products obtained when 5-c hloro-4-formylpyrazoles are reacted with azide ion all seem to be form ed by a common mechanism, via substituted 2-cyano-3-azo propenals or a zwitterionic intermediate. The nature of the products is determined b y the position of nucleophilic attack at the intermediate. Structural characterization of the products has been obtained by NMR spectroscopy and single-crystal X-ray crystallography.