Reactions with Heterocyclic Diazonium Salts, II Synthesis of Some New Pyrazolo[1,5-c]-as-triazines and 1,2,4-Triazolo[1,5-c] -as-triazines

Abstract

3-Phenylpyrazole-5-diazonium chloride (2) couples with benzoylacetonitrile and with phenacylthiocyanate to yield the corresponding hydrazone derivatives 3 a, b. Whereas 3 a cyclised into the pyrazolo[1,5-c]-as-triazine derivative (4a) upon treatment with concentrated sulphuric acid via elimination of water, treatment of 3 b with the same reagent under the same conditions has resulted in elimination of thiocyanic acid and the formation of the pyrazolo[1,5-c]-as-triazine derivative (4b). Treatment of 2 with aqueous sodium acetate has afforded the corresponding 3-phenyl-5-diazopyrazole (6). The latter reacted readily with dipolarophiles to yield pyrazolo- [1,5-c]-as-triazine derivatives. Pyrazolo[1,5-c]-as-triazines has also been formed upon treatment of 6 with active methylene compounds. The mechanism of reaction of 2 and 6 with active methylene compounds is discussed. Diazotization of 5-amino-3-ethyl-1,2,4-triazole nitrate (7) has afforded the corresponding diazonium derivative which coupled with benzoylacetonitrile and with acetoacetanilide to yield the corresponding hydrazones 9 a, b. The latter could be cyclised into 1,2,4-triazolo[1,5-c]-as-triazines by the action of concentrated sulphuric acid