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Paper | Special issue | Vol 93, No. 2, 2016, pp.628-646
Published online, 7th January, 2016
DOI: 10.3987/COM-15-S(T)46
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

Viktor A. Zapol'skii, Jan C. Namyslo, Mimoza Gjikaj, and Dieter E. Kaufmann*

*Institute of Organic Chemistry, Clausthal University of Technology, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany

Abstract

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-f]indazole-4,8-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-f]indazole-4,8(1H,6H)-dione (9) has been confirmed by X-ray analysis.