Vinylimidazoles Research Articles

Synthesis of electron-poor N-Vinylimidazole derivatives catalyzed by Silica nanoparticles under solvent-free conditions

A B S T R A C T: Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and acetylenic esters, by NH-acids such as azathioprine, imidazole or theophylline leads to the formation of vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce phosphorus ylides. Silica nanoparticles (silica NPs were prepared by thermal decomposition of rice hulls) was found to catalyze the conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90 o C, 30 min) conditions. It may be speculated that the polar amphoteric surface (OH groups of the silica NPs) facilitates the interaction of adsorbed weak acidic and basic components due to stabilization of the corresponding transition states and intermediates by H-bonding. It seems that the interactions with the neighboring silanol groups are plausible factors in the rate acceleration. Participation of two proximate silanol groups (one as an Hbond donor and the other as an H-bond acceptor) in the reaction mechanism also seems to be plausible.

Erratum to: “Intramolecular Specific Interaction C-H…O in 1-vinyl-5-pyrazolecarboxylic Acid Revealed by 1H NMR Spectroscopy Data”

A. O. Baltayana, A. A. Saakyana, O. S. Attaryanb, and G. V. Asratyanb a Institute of Organic Chemistry, National Academy of Sciences of Armenia, ul. Zakaria Sarkavagi 167a, Yerevan, 0091 Armenia e-mail: angelabaltayan@mail.ru b Institute of Applied Chemistry ARIAK, Yerevan, Armenia Received February 6, 2013

Syntheses and Crystal Structures of Three Electron Poor N-Vinyltheophylline Derivatives

Protonation of the highly reactive 1:1 interme- diates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or dialkyl acetylenedi- carboxylates) by theophylline leads to vinyltriphenylpho- sphonium salts, which undergo Michael addition reaction with conjugate base to produce phosphorus ylides. Silica gel was found to catalyze conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90 � C, 1 h) conditions. The structures of these compounds were confirmed by IR, 1 H, and 13 CN MR spectroscopy, and single crystal X-ray structure determina- tion. The structural analysis of the products indicated that the reaction is completely regio- and stereoselective.

Triphenylphosphine-Catalyzed Preparation of Sterically Congested, Electron-Poor N-Vinylimidazole Derivatives from Acetylenic Esters and Imidazole-Containing NH-Acids

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or ethyl 3-phenyl-2-propynoate), by azathioprine or imidazole leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce phosphorus ylides.Dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and potassium iodide were found to catalyze the conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90°C, 1 h) conditions. The structural analysis of the products indicated that the reaction is regio- and stereoselective.

ChemInform Abstract: Synthesis and Antifungal Activities of a Series of (1,2-Disubstituted Vinyl)imidazoles.

A series of vinylimidazoles containing a hetero atom such as sulfur or oxygen at a β-position of the vinyl group was prepared and the antifungal activities were tested. It was found that sulfur-substituted derivatives such as (E)-1-[2-(methylthio)-1-[2-(pentyloxy)phenyl]ethenyl]-1H-imidazole (5a-5) and (E)-1-[1-[2-(hexyloxy)phenyl]-2-(methylthio)ethenyl]-1H-imidazole (5a-6) showed exvellent antifungal activities against dermatophytes and yeast cells. The stereochemistry of the hydrochloride salt of 5a-5 was determined by X-ray crystallography. The structure-activity relationships were discussed.

Copolymerization of N-vinylcaprolactam with N-vinyl(benz)imidazoles and the properties of aqueous solutions of the copolymers

The free-radical solution copolymerization of N-vinylcaprolactam with 1-vinylimidazole, 1-vinyl-2-methylimidazole, 1-vinyl-2-methyl-3-propylimidazolium iodide, or 1-vinyl-2-methylbenzimidazole was investigated and the monomer reactivity ratios in the copolymerization were calculated. It was shown that 1-vinylimidazole exhibits a relatively higher activity in the copolymerization as compared to the monomers that bear substituents on the ring. It was established that, except for the copolymers of 1-vinyl-2-methylbenzimidazole, water-soluble products could be obtained. Aqueous solutions of N-vinylcaprolactam copolymers with N-vinyl(methyl)imidazoles were found to have a higher phase separation temperature relative to poly(N-vinylcaprolactam) solutions. The thermal stability of the aqueous solutions increases with a rise in the amount of hydrophilic 1-vinyl-and 1-vinyl-2-methylimidazole units in macromolecular chains and in the presence of NaCNS or KBr. The effect of salts on the thermal stability of aqueous copolymer solutions has the same character as in the case of the N-vinylcaprolactam homopolymer.

Adsorption of partially quarternised poly(vinyl imidazoles) onto SiO 2 and Y 2O 3

Partially quarternised poly(vinyl imidazoles) (PVIs) were synthesised and their adsorption at pH 10, where only the quarternary groups are charged, was studied. The adsorbed amount is much higher on SiO 2 surfaces than on Y 2O 3 surfaces. Nevertheless, in 10 −2 M KNO 3 solutions the maximum adsorbed amount of PVI on both surfaces, measured as a function of the degree of quarternisation, exhibits a maximum between 4% and 7% positively charged groups. The hydrodynamic layer thickness of adsorbed PVI has a maximum at the same degree of quarternisation. Moreover, the maximum coincides with the isoelectric point of the SiO 2 or Y 2O 3 particles bearing adsorbed PVI. At degrees of quarternisation higher than 7%, the zeta-potentials of PVI-covered SiO 2 and Y 2O 3 particles are identical. The colloidal stabilisation mechanism of these particles is steric at low (< 10%) degrees of PVI quarternisation, and changes to an electrosteric mechanism at higher degrees of quarternisation. Increasing the salt concentration leads to a small shift in the adsorption maximum to higher degrees of quarternisation. At quarternisation degrees of less than 4%, the adsorption decreases markedly with increasing salt concentration, while at higher degrees of quarternisation the adsorption increases only slightly with salt concentration.

The use of vinyl imidazoles as Diels-Alder dienes

The first use of a vinylimidazole as a Diels-Alder diene is reported. Semiempirical calculations are used to characterize 1-methyl-5-vinylimidazole as an electron-rich diene.

1-Vinyl-2-hydroxymethylimidazoles and some of their transformations

1. 1-Vinyl-2-hydroxymethylimidazole and 1-vinyl-2-hydroxybenzimidazole were synthesized by the condensation of 1-vinylimidazoles with paraform. The compounds were subjected to hydrochlorination, hydrogenation, and polymerization. 2. The 1-vinyl-2-hydroxymethylimidazoles react with acetylene under pressure to give the imidazole N,O-divinyl derivatives.

Synthesis of N-Vinylimidazoles and Orientation of their 1, 4-and 1, 5-Isomers

加圧アセチレンとイミダゾールとの付加反応を主としてジオキサン-2-プロパノール混合溶媒中で行ない,多くのN-ビニルイミダゾールを合成した。そのさい,4-位に置換基を有するイミダゾールからは互変異性により二つのN-ビニル異性体からなる異性体混合物が生じたので,各異性体を単離し,水素化によりN-エチル体としたのち,ニトロ化物を経由し,α-アミノ酸へ誘導して各異性体の置換基位置を決定した。一方,このようにして置換基位置が明らかにされた各異性体のNMRスペクトルと,それらのニトロ誘導体の紫外吸収スペクトルを検討し,おのおののスペクトルにより置換基位置の決定が,この場合簡単に行なえることを確かめた。