1- Pyridin-2-ylpyrazol-3-ones

The new podand ligand hydrotris[3-(6-methyl)pyridin-2-ylpyrazol-l-yl]borate, (Tp2< 6Me py), has been reported by McCleverty and Ward.171 It possesses a methyl group attached to the C6 positions of the pyridyl rings, which interferes when the ligand is coordinated in a fully hexadentate manner. In fact, [M(Tp216Melpy)(N03)2(H20)] (M = Eu, Tb or Gd) (Fig. 1.21) showed partial dissociation of the podand occurring to relieve potential steric problems either one or two of the pyridyl groups are not coordinated, such that Tp2(6Me,py... 

Scheme 53). 3-Ethoxyacrylic acid N -phenylhydrazide 233 cyclized by intramolecular conjugate substitution of ethoxide ion when treated with aqueous hydrochloric acid to give l-pyridin-2-ylpyrazol-3-one 234 in 45% yield (04JMC4645). 

Sammour (72JPR612) (Scheme 20) reported that the Mannich reaction of 5-pyridin-3-ylpyrazol-3-one 65 with primary amines such as the methylamine, ethylamine, aniline, 4-toluidine, 4-chloroaniline or 4-methoxyaniline and paraformaldehyde, gave the corresponding 4-[(alkyl or arylamino)methyl]-5-pyridin-3-ylpyrazol-3-one 66 in moderate yields. 

Three examples of N1 acylation of a l,2-dihydropyrazol-3-one have been reported. Benzoylation of 2-phthalazin-l-ylpyrazol-3-one 97a was accomplished by heating in pyridine containing benzoyl chloride to give l-benzoylpyrazol-3-one 98a in 55% yield (81PHA471). On the other hand acetylation of pyrazol-3-ones 97b,c occurred by heating in acetic anhydride to afford l-acetylpyrazol-3-ones 98b,c in excellent yields (91JCS(CC)314, 96T1579) (Scheme 31). 

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See also in sourсe #XX -- [ ]

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