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Chapter 3
Synthesis of trisubstituted pyrazoles/isoxazoles
3.3 Synthetic methods for the pyrazole and isoxazole derivatives
There are several methods reported in the literature for the preparation of
pyrazoles and isoxazoles described as under.
Pranab K. Mahata et al. 29 has synthesized 3-dimethoxymethyl-5-(methylthio)
pyrazole/ isoxazole derivative (Figure-12) shown to be useful three carbon synthon
for efficient regiospecific synthesis of a variety of five (pyrazole/isoxazole) with mask
or unmask aldehyde functionality by cyclocondensation with bifunctional
nucleophiles such as hydrazine and hydroxylamine respectively.
Figure-12
Sabine Kuettel et al. 30 has synthesized 4-(3-phenylpyrazole/isoxazol-5-
yl)morpholine derivatives (Figure-13) by two synthetic routes, in which substituted
acetophenones were reacted with carbon disulfide and methyl iodide in the presence
of sodium hydride to give 4-phenoxyphenyl-2,2-bis(methylthio)vinylketones,
followed by in situ cyclization of the resulting N,S-acetals with hydrazine
hydrate/hydroxylamine.
Figure-13
Scott R. Tweedie et al. 31 has synthesized a pyrazole and isoxazole derivatives
via palladium-catalyzed couplings of heteroaryl amines with aryl halides using
sodium phenolate as the stoichiometric base (Figure-14).
Figure-14
Department of Chemistry Saurashtra university, Rajkot-360005 89