Synthesis of α-methyl-β-(3-methylpyrazol-1-yl)-and α-methyl-β-(5-methylpyrazol-1-yl)propionic acids and their esterification with vinyl acetate

α-Methyl-β-(3-methylpyrazol-1-yl)-and α-methyl-β-(5-methylpyrazol-1-yl)propionic acids were synthesized by reaction of 3(5)-methylpyrazole with methyl methacrylate, followed by separation of the resulting isomeric esters and their hydrolysis. Esterification of the title acids was performed via vinyl exchange reaction with vinyl acetate in the catalytic system mercury acetate-trifluoroacetic acid.     

Excitation of the 3p3Πu level of H2 by electron impact; pressure effects

The excitation cross-section of the 3p³Π_u level of H₂ has been measured for electrons from energy threshold to 100 eV. We compare the intensities of the emitted lines to the Balmer lines whose excitation cross-sections from H₂ are known. The effects of dissociation, cascade, polarisation and pressure are discussed. The maximum excitation cross-section is found to be 3·30 × 10^-18 cm² ± 50% at 22·5 eV.     

Synthesis and structure of 1-(buta-1,3-dien-2-yl)pyrazoles and their behavior in Diels-Alder reactions

A convenient procedure has been developed for the synthesis of cis-and trans-isomeric 1-(buta-1,3-dien-1-yl)-1H-pyrazoles by reaction of the corresponding pyrazoles with β-methylacrolein diethyl acetal and subsequent 1,4-cleavage of the nucleophilic substitution products. The behavior of the title compounds in Diels-Alder reactions with maleic anhydride has been studied. According to the ¹H NMR data, 1-(buta-1,3-dien-1-yl)-1H-pyrazole is a mixture of cis and trans isomers. Butadienylpyrazoles having methyl groups in the pyrazole ring do not react with maleic anhydride.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-vinylazoles from vinyl acetate without using mercury catalysts

N-Vinyl-substituted pyrazole, 3(5)-methylpyrazole, imidazole, and 1,2,4-triazole were synthesized by addition of the corresponding azoles to vinyl acetate under conditions of phase-transfer catalysis, followed by pyrolysis of N-(1-acetoxyethyl)azoles thus formed at 350–400°C in the presence of water.     

Diels-Alder reactions of 3-and 5-methyl-1-vinylpyrazoles with cyclohexa-1,3-diene and hydrogenation of the reaction products

The behavior of isomeric vinylpyrazoles in the Diels-Alder reactions with cyclohexa-1,3-diene was studied to show that the spatial location of the vinyl group on the N² atom does not affect the diene synthesis.     

13C NMR spectra of 4-hydroxymethylpyrazoles and their chemical behavior at heating

It was established that in the ¹³C NMR spectra of 4-hydroxymethylpyrazoles the carbon atom of hydroxymethyl group of 1,3,5-trimethyl-4-hydroxymethylpyrazole is deshielded by 6.28–6.78 ppm compared to 1-methyl-4-hydroxymethyl-, 1,3-dimethyl-4-hydroxymethyl- and 1,5-dimethyl-4-hydroxymethylpyrazoles. It is assumed that this difference is related to their dissimilar behavior at heating.