Spectroscopic evidence of donor-acceptor interactions of 1-ethyl- and 1-vinylpyrazoles

Chípanina, N. N.; Kazakova, N. A.; Shestova, L. A.; Domnina, E. S.; Skvortsova, G. G.; Frolov, Yu. L.

doi:10.1007/bf00608819

Cited by 2 publications

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Section: Short Communicationsmentioning

confidence: 99%

“…If pyrazole molecule contains another nucleophilic center, e.g., double C=C bond, their reactions with hydrohalic acids could follow two pathways. Hydrochlorination of 1-alkenylpyrazoles occurs at the N 2 atom only on cooling (-70°C), whereas at room temperature the process involves the alkenyl substituent [5,6].We were the first to reveal that acetalization of pyrazole-4-carbaldehydes Ia-Ic with 2-sulfanylethanol in the presence of 5-6 equiv of chlorotrimethylsilane at room temperature leads to the formation of the corresponding dithioacetal hydrochlorides IIa-IIc in good yield. Protonation of the N 2 atom in the heteroring of compounds IIa-IIc is indicated by the presence in their IR spectra of a broadened NH + absorption bands at 2500-2800 cm -1 .…”

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confidence: 96%

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Unexpected formation of pyrazolecarbaldehyde dithioacetal hydrochlorides

et al. 2011

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SHORT COMMUNICATIONSPyrazoles are important building blocks in the synthesis of novel pharmaceutical agents possessing analgesic, antiphlogistic, antibacterial, antidepressant, and other kinds of biological activity [1], as well as of insectoacaricides [2], dyes, luminophores, and ligands [3]. Water-soluble pyrazole derivatives are of particular significance. The ability of pyrazoles to form hydrohalides is determined by the presence of a pyridinetype nitrogen atom in their molecules, which possesses enhanced nucleophilicity [4]. It is known that pyrazole hydrochlorides are unstable. If pyrazole molecule contains another nucleophilic center, e.g., double C=C bond, their reactions with hydrohalic acids could follow two pathways. Hydrochlorination of 1-alkenylpyrazoles occurs at the N 2 atom only on cooling (-70°C), whereas at room temperature the process involves the alkenyl substituent [5,6].We were the first to reveal that acetalization of pyrazole-4-carbaldehydes Ia-Ic with 2-sulfanylethanol in the presence of 5-6 equiv of chlorotrimethylsilane at room temperature leads to the formation of the corresponding dithioacetal hydrochlorides IIa-IIc in good yield. Protonation of the N 2 atom in the heteroring of compounds IIa-IIc is indicated by the presence in their IR spectra of a broadened NH + absorption bands at 2500-2800 cm -1 . Hydrochlorides IIa-IIc are colorless water-soluble oily substances that are stable under usual conditions. 4-Bis(2-hydroxyethylsulfanyl)methyl-3,5-dimethyl-1H-pyrazole hydrochlorides IIa-IIc (general procedure). 2-Sulfanylethanol, 0.156 g (2 mmol), was added dropwise under stirring to a mixture of 1 mmol of pyrazolecarbaldehyde Ia-Ic and 0.77 ml (6 mmol) of chlorotrimethylsilane. The reaction was accompanied by heat evolution, and the mixture divided into two layers. The mixture was stirred for 15-20 min at room temperature, the upper layer was separated, and the viscous residue was washed with hot hexane and with diethyl ether and dried under reduced pressure. S,S′-[(1-Isopropyl-3,5-dimethyl-1H-pyrazol-4-yl)-methanediyl]bis(2-sulfanylethanol) hydrochloride (IIa). Yield 0.315 g (93%). IR spectrum (film), ν, cm -1 : 3339 br (OH), 2713-2540 br (NH + ). 1 H NMR spectrum, δ, ppm: 1.57 d [6H, CH(CH 3 ) 2 , 3 J = 6.7 Hz], 2.55 s and 2.56 s (3H each, CH 3 ), 2.69 d.t and 2.82 d.t (2H each, CH 2 S, 2 J = 14.1, 3 J = 6.3 Hz), 3.70 d.t and 3.76 d.t (2H each, CH 2 O, 2 J = 11.3, 3 J = 6.3 Hz), 4.91 m (1H, NCH), 5.44 s (1H, SCHS). 13 C NMR spectrum, δ C , ppm: 10.43 and 10.63 (CH 3 ), 21.47 [CH (CH 3 ) 2 ], 36.20 (CH 2 S), 43.54 (SCHS), 53.67 (NCH), 62.79 (OCH 2 ), 119.96 (C 4 ), 144.70 and 145.56 (C 3 , C 5 ). Found, %: C 45.76; H 7.38; Cl 10.38; N 8.21; R = i-Pr (a), CH 2 =CHCH 2 (b), PhCH 2 (c).

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Section: Short Communicationsmentioning

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Unexpected formation of pyrazolecarbaldehyde dithioacetal hydrochlorides

et al. 2011

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“…Vinylpyrazoles coexist with pyrazole and show no tendency to add it back. The shelf life of vinylpyrazoles is good, and no polymerization in the neat liquid is observed even after 2 years [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Some reactions with vinylpyrazoles have been described in the literature.…”

Section: Reactivity Of Vinylpyrazolesmentioning

confidence: 99%

“…Furthermore, these compounds present interesting physicochemical properties, such as tautomerism and isomerism, owing to the presence of the vinyl group. Consequently, several spectroscopic studies on vinylpyrazoles have been reported [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. For example, Skvortsova and coworkers performed several 1 H- and 13 C-NMR spectral analyses for evaluation of electronic and steric effects in 1-vinylpyrazoles [ 28 ].…”

Section: Introductionmentioning

confidence: 99%

Revisiting the Chemistry of Vinylpyrazoles: Properties, Synthesis, and Reactivity

Silva

2022

Molecules

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Vinylpyrazoles, also known as pyrazolyl olefins, are interesting motifs in organic chemistry but have been overlooked. This review describes the properties and synthetic routes of vinylpyrazoles and highlights their versatility as building blocks for the construction of more complex organic molecules. Concerning the reactivity of vinylpyrazoles, the topics surveyed herein include their use in cycloaddition reactions, free-radical polymerizations, halogenation and hydrohalogenation reactions, and more recently in transition-metal-catalyzed reactions, among other transformations. The current state of the art about vinylpyrazoles is presented with an eye to future developments regarding the chemistry of these interesting compounds. Styrylpyrazoles were not considered in this review, as they were the subject of a previous review article published in 2020.

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Spectroscopic evidence of donor-acceptor interactions of 1-ethyl- and 1-vinylpyrazoles

Cited by 2 publications

References 1 publication

Unexpected formation of pyrazolecarbaldehyde dithioacetal hydrochlorides

Unexpected formation of pyrazolecarbaldehyde dithioacetal hydrochlorides

Revisiting the Chemistry of Vinylpyrazoles: Properties, Synthesis, and Reactivity

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