3,6,6-trimethyl-4-oxo-1-(2-pyridyl)-4,5,6,7-tetrahydroindazole in Schmidt reaction and Beckmann rearrangement conditions for the 4-hydroxyimino derivative

Recent Advances in the Chemistry of Indazoles

“…Aromatization of 4‐hydroxyimino‐6,6‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydroindazole ( 123 ) to 124 was accomplished by heating in PPA. The proposed mechanism proceeds via the formation of an iminium cation, followed by subsequent hydride and methyl migration, and final oxidation to indazole 124 (Scheme ) 121…”

Oximes of five-membered heterocyclic compounds with two heteroatoms 2. Reactions and biological activity (Review)

“…The reaction of 4-hydroxyimino-6,6-dimethyl-1-phenyl(or 2-pyridyl)-4,5,6,7-tetrahydroindazoles 38 with polyphosphoric acid takes place with migration of the methyl group and reduction of the oxime group to an amino group [86] leading to aromatization products 39. Imidazole, pyrazole, and benzisoxazole aldoximes are converted into nitriles in the presence of NBS/triethylamine [87], acetic anhydride [88], or PCl 3 /Et 3 N/MeCN [89].…”

Synthesis and transformations of perfluoroalkyl-containing 6,7-dihydro-1H-indazol-4(5H)-ones oximes

“…The Beckmann rearrangement of oximes with the generation of corresponding amides is their most characteristic reaction. However it is known that heating non-fluorinated 3-alkyl-1-aryl-6,6-dimethyl-6,7-dihydro-1H-indazol-4(5H)-one oximes in polyphosphoric acid (PPA) at 120-130°С results either in a classic Beckmann rearrangement giving 3-alkyl-5-oxo-1-phenyl-1,4,5,6,7,8-hexahydropyrazolo [4,3-b]azepines, or in Semmler-Wolff aromatization providing 4amino-3-alkyl-5,6-dimethyl-1-aryl-1Н-indazoles depending of the alkyl substituent structure [28,29]. By heating 3-trifluoromethyl-6,6-dimethyl-1-aryl-6,7dihydro-1H-indazol-4(5H)-one oximes 2a and 2d in PPA at 120°С for 15 h followed by treating with 20% aqueous HCl we obtained hydrochlorides of 4-amino-1-aryl-5,6-dimethyl-1Н-indazole-3-carboxylic acids 5a and 5b, and the heating of the indazolone oximes 2b, 2c, 2e and 2f containing perfluoroethyl and perfluoropropyl groups in the same conditions for 8 h followed by treating with 20% aqueous ammonia afforded of 1-(4-amino-1-aryl-5,6-dimethyl-1Н-inda-zol-3-yl)fluoroalkan-1-ones 6a-6d.…”