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Saunders, Keith John (1964) Reactions of some unsaturated pyrazole compounds. Doctoral thesis, Northern Polytechnic.
1-Phenyl-4-vinylpyrazole has been prepared by decarboxylation of p-(1-phenyl-4-pyrazolyl)acrylic acid. The vinyl compound was treated with bromine to give the dibromide, which was found to react with aqueous ethanolic potassium hydroxide to form 4-acetyl-1-phenylpyrazole; possible steps involved in this unusual reaction have been suggested. 1-Phenyl-4-vinylpyrazole has also been polymerised.
The unsaturated pyrazole compounds, 1-phenyl-4-vinylpyrazole and p-(1-phenyl-4-pyrazolyl)acrylic acid and its ethyl ester have been treated with o-nitrobenzenesulphenyl chloride. Comparison of these reactions with those of the benzene analogues has shown a number of differences. 1-Phenyl-4-vinylpyrazole and styrene both gave addition products, but the pyrazole adduct readily eliminated hydrogen chloride whereas the benzene analogue was relatively stable. The pyrazole acid gave an unsaturated thio-acid, but with cinnamic acid the only product isolated was bis-o-nitrophenyl disulphide. The pyrazole ester gave an unsaturated thio-ester in good yield whereas ethyl cinnamate gave a product which, on hydrolysis, gave a poor yield of a thiocinnamic acid.
Michael condensations between diethyl malonate and various unsaturated pyrazoles with the structure R1CH = CR2R3 (R1 = 1-phenyl-4-pyrazolyl) have been investigated. With R2 = H and R3 = CO2Et; COMe; COPh and R2 = R3 = C02Et no condensation products were isolated. The reactions between the pyrazoles and ethyl acetoacetate were also investigated; condensation occurred with only the pyrazolyl di-ester. It has been shown that, under similar conditions, the benzene analogues generally undergo condensation more readily.
Ethyl p-(1-phenyl-4-pyrazolyl)acrylate has been treated with the Grignard reagents, phenylmagnesium bromide and methylmagnesium iodide. The reaction products isolated suggest that only 1,2- addition occurs under the conditions used. This is in contrast to the benzene analogue which also undergoes 1,4- addition.
β-(1-Phenyl-4-pyrazolyl)acrylic acid and its ethyl ester have been reduced with lithium aluminium hydride to give an unsaturated alcohol. This contrasts with reduction of the benzene analogues, which generally leads to a saturated alcohol.
The following new compounds have been prepared and characterised:
1-Phenyl-4-vinylpyrazole
1,2-Dibromo-2-(1-phenyl-4-pyrazolyl)ethane
2-Bromo-1-(1-phenyl-4-pyrazolyl)ethanol hydrobromide
4-Bromoacetyl-1-phenylpyrazole
1-Chloro-2-o-nitrophenylthio-1-(1-phenyl-4-pyrazolyl)ethane
1-o-Nitrophenylthio-2-(1-phenyl-4-pyrazolyl)ethylene
1-Chloro-2-o-nitrophenylthio-1-phenylethane
α-o-Nitrophenylthio-β-(1-phenyl-4-pyrazolyl )acrylic acid
Ethyl a-o-nitrophenylthio-β-(1-phenyl-4-pyrazolyl)acrylate
2-o-Nitrophenylthiocinnamic acid
Ethyl 1-phenyl-4-pyrazolylmethylidenemalonate
Ethyl 4,6-dioxo-2-(1-phenyl-4-pyrazolyl)cyclohexane-1,3- dicarboxylate
1,3-Diphenyl-3-(l-phenyl-4-(l-phenyl-4-pyrazolyl)prop-1-one
2-Methyl-4-(1 -phenyl-4-pyrazolyl)but-3-en-2-ol
3-(1-Phenyl-4-pyrazolyl)prop-2-en-l-ol and its p-Nitrobenzoate
β-(1-Phenyl-4-pyrazolyl)acraldehyde
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