Aminopyrazoles and-indazoles

3- and 5-Aminopyrazoles are very useful as starting materials for the syntheses of various fused ring systems. Many specific examples of these pyrazole fused ring systems can be found in Section 4.01.11. 

Diazotization of 4-amino-5-alkynylpyrazole 335 followed by intramolecular cyclization gave 7-chloro-17/-pyr-azolo[4,3-f]pyridazines 336 the amino and alkynyl positional isomers at the C-3 and C-4 positions were also cyclized to give other pyrazolopyridazines (Equation 64) 1998F1C0519 . Diazotization of 4-aryl-5-aminopyrazoles (aryl = 4,5-dimethoxyphenyl and indol-3-yl) followed by intramolecular azo coupling reactions led to the corresponding pyrazolo[3,4-f]cinnolines or pyrazolo[3, 4 6,5]pyridazino[3,4-. ]indoles 2004CHE1506 . 

Diazotization of 5-aminopyrazole 337 in acetic acid afforded 37/-pyrazolo[3,4-f]cinnoline 338 via intramolecular azo coupling while diazotization in sulfuric acid in the presence of arenes resulted in the formation of 5-arylazopyr-azoles 339 (Equation 65) 2004CFIE964 . 

Substituted 3-anilino-l,5-diphenylpyrazoles were oxidized with lead(iv) tetraacetate in benzene or methylene chloride solution 1997M261 . ESR measurements confirmed the formation of aminyl radicals from /irzra-CFIs-substituted pyrazoles. The radical intermediates from unsubstituted pyrazoles were recognized by their transformations to triarylaminium cation radicals. These were generated by consecutive oxidation of the dimeric products the structures of which were proved by NMR spectroscopy and labeling. 

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