4-Hydrazono pyrazol-3-ones

The mesomeric diazo compound lOOa/lOOb, derived from diazo group transfer to the appropriate pyrazol-3-one, was irradiated for 10 h in tetrahydrofuran to give the hydrazone chelated adduct 101 as the only product (78H199) (Scheme 29). Mesomeric lOOa/lOOb reacts also with triphenylphosphine to give intermediate ( /Z)-phosphazine 102 which is extremely sensitive to water and hydrolyzes to EjZ)-hydrazone 103. 3-Hydroxy-5,5-dimethyl-cyclohex-2-enone 104 and 3-hydroxy-inden-1-one 106 readily couple with lOOa/lOOb in the presence of sodium acetate to give hydrazono derivatives 105 and 107, respectively. 

By the cyclization of hydrazones. A common characteristic of hydrazone cyclizations is the requirement of high temperatures when no solvents are used. Under these conditions, heating 3-[(Z)-2-(f-butyl-substituted silyl)hydrazono]butanoates 71a-c at 200 °C initially formed pyrazol-3-ones 72a-c which were not stable at that temperature but underwent a l,3-N,0-silyl group migration to the O-silylpyrazoles 73a-c (99JOM341) (Scheme 18). 

Wejroch et al. (02PJC1577) (Scheme 21) heated 3-[(4,4-dimethyl-6-oxopyridazin-3-yl)hydrazono]butanoate 85 at 140-175 °C and obtained a mixture of 6-(3-oxo-pyrazol-2-yl)pyridazin-3-one 86 and [l,2,4]tri-azolo[4,3-bJpyridazin-6-(5H)-one 87 in 24% and 68% yield, respectively. Interestingly, 3-[(5-phenyl-6-oxopyridazin-3-yl)hydrazono]butanoate 88 was heated at a higher average temperature to give 6-(3-oxopyrazol-2-yl)-pyridazin-3-one 89 as the only detected product in 37% yield. The authors... 

To prepare 5-amino-4-[(3-phenyl-lH-pyrazol-4-yl)hydrazono]-2,4-dihydropyrazol-3-one 212, Al-Mousawi et al. (08ARK268(xvi)) diazotized 3-phenyl-lH-pyrazol-4-ylamine 209 in hydrochloric acid to yield, in situ, diazonium chloride 210 which then coupled with malononitrile to give 2-pyrazolylhydrazonomesoxalonitrile 211. Compound 211 then could be... 

From 3-bromo(or chloro)-4-methoxychromen-2-one. Okamoto and co-workers (99JHC767) (Scheme 87) described an efficient method of converting chromen-3-ones 387a,b into 4-bromo(or chloro)-l,2-di-hydro-5-(2-hydroxyphenyl)pyrazol-3-ones 390a,b and 4-hydrazono(or... 

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