Chemistry of Polyhalogenated Nitrobutadienes, 15: Synthesis of Novel 4-Nitro-3-amino-1H-pyrazole-5-carbaldehydes and Pyrazolo[3,4-f]indazole-4,8-diones

Condensation of 1-amino-1-(1H-benzo[d][1,2,3]triazol-1-yl)-3,4,4-trichloro-2-nitrobuta-1,3-dienes 3a-e with methylhydrazine leads to a series of uniquely persubstituted 4-nitropyrazoles 4a-e bearing a dichloromethyl substituent in 5-position. Subsequent hydrolysis of this group applying aqueous sulfuric acid then gives interesting push-pull substituted pyrazole-5-carbaldehydes 5a-e. Upon hydrolysis of 4a-e at harsher reaction conditions different pyrazolo[3,4-Aindazole4,8-diones were also formed. A mechanism of the homo-condensation of carbaldehydes 5a,d to the indazole derivatives 8-13 is proposed, and as an example the structure of 3,7-bis(dimethylamino)-1,6-dimethylpyrazolo[3,4-Aindazole4,8(1H,6H)-dione (9) has been confirmed by X-ray analysis.