Di-isotacticity of poly(methyl propenyl ether) and double-bond opening of methyl propenyl ether in cationic polymerization

The di-isotacticity of poly(methylpropenyl ether) obtained by the cationic polymerization has been studied by NMR spectra. The NMR spectra of β-methyl protons of the polymer are decoupled from the β-methine proton spectra to determine the di-isotactic fraction in a polymer. The signals of β-methyl protons at 8.78 and 8.89 τ are estimated as spectra based on threo- and erythro-di-isotactic diads, respectively. With BF₃·O(C₂H₅)₂ as a catalyst, the trans monomer yields a crystalline polymer and its structure is threo-di-isotactic. Otherwise, cis monomer produces an amorphous polymer, and it is a mixture of threo- and erythro-di-isotactic structure. From these results, it is concluded that the double bond in trans monomer is opened exclusively in the cis type, and in cis monomer cis- and trans-openings take place at almost the same rate.     

Nigellamines A3, A4, A5, and C, new dolabellane-type diterpene alkaloids, with lipid metabolism-promoting activities from the Egyptian medicinal food black cumin

New dolabellane-type diterpene alkaloids, nigellamines A(3), A(4), A(5), and C, were isolated from the methanolic extract of an Egyptian medicinal food, black cumin (the seeds of Nigella sativa). Their absolute configurations were determined on the basis of chemical and physicochemical evidence. Nigellamines were found to lower triglyceride levels in primary cultured mouse hepatocytes, and in particular, the activity of nigellamine A(5) was equivalent to that of the hypolipidemic agent, clofibrate.     

Electronic spectra of 12-S-CIS conformationally locked retinals

The electronic absorption spectra of the four new 12-$\text{s}$-$\text{cis}$-locked retinals (1a–1d) bearing 7-$\text{trans}$, 11-$\text{trans}$ double bond geometries are described and compared with those of analogous 7-$\text{trans}$, 11-$\text{cis}$-geometries (1e–1h) and parent retinals (2a-h).     

Remarkable tris(trimethylsilyl)silyl group for diastereoselective [2 + 2] cyclizations

[reaction: see text] Diastereoselective [2 + 2] cyclizations of aldehyde- and ketone-derived silyl enol ethers with acrylates is described. The use of the tris(trimethylsilyl)silyl group allows for unprecedented reactivity, yields, and selectivity for these cyclizations. The presence of silicon-silicon bonds proved to be important for this transformation, where typical silyl groups (TBS and TIPS) failed to give any desired product. The bulky bis(2,6-diphenylphenoxide) aluminum triflimide catalyst was essential for high diastereoselectivity.     

New efficient route for solid-phase synthesis of benzimidazole derivatives

A simple and efficient method for the solid-phase synthesis of benzimidazole libraries is described. Monoalkylation of various o-phenylenediamines on resin-bound bromoacetamide proceeded smoothly to give the monoalkyl resin-bound o-phenylenediamines in high yields. Subsequent cyclization of the diamines with various aldehydes afforded solid-supported benzimidazoles. Cleavage from the resin gave benzimidazoles in good yields. The present method enabled the introduction of the diversity on the benzene ring of imidazoles. Azabenzimidazoles, such as 4-azabenzimidazoles, 5-azabenzimidazoles, and purines, were also synthesized in good yields with high purities by the same procedure.     

Effects of metal salts on polymerization. VI. Photo and thermally catalyzed polymerization of N-vinylimidazole in the presence of metal salts

Polymerization of 2-methyl-1-vinylimidazole (MVI) and 2-ethyl-1-vinylimidazole (EVI) was found to be markedly photosensitized in the presence of oxidizing metal salts such as UO₂(NO₃)₂, Ce(NH₄)₂(NO₃)₆, Hg(CH₃COO)₂, AgNO₃; non-oxidizing metal salts such as Zn^II did not act as photosensitizers. The interaction of monomer with a metal salt is discussed on the basis of infrared and electronic spectroscopy. This photopolymerization is very specific with respect to the kind of monomer. The polymerization of noncomplexing monomer (styrene) is not photosensitized by these metal salts. Consequently, photosensitized electron transfer between monomer and metal salt via complex formation is considered to be the most probable initiation mechanism. Cupric acetate and sodium chlorolaurate, which have been reported as efficient initiators for the polymerization of vinylpyridine and N-vinylcarbazole, respectively, act as linear terminators of growing radicals. The radical polymerizability of the zinc complex of MVI was studied by means of copolymerization with styrene. The reduction of the reactivity of MVI on complexing was explained by correlating with the spectroscopic observations. Because the polymerization system is heterogeneous, a detailed discussion was not possible.     

Acidic properties of V2O5-WO3/ZrO2 catalysts

The adsorption of pyridine on V₂O₅−WO₃/ZrO₂ has been studied by FTIR. In V₂O₅/ZrO₂ (2 wt.%), the number of both Br?nsted and Lewis acidic sites increased with the addition of WO₃, while in V₂O₅/ZrO₂ (5 wt.%), Br?nsted sites increased and Lewis sites did not change.     

Cross-coupling of alkenyl,aryl or allylic selenides and grignard reagents catalyzed by nickel-phosphine complexes

Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields. The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl₂ [Ph₂PCH₂CH₂CH₂PPh₂] was found to be PhSeMe « PhCl > PhSMe by the competitive reactions.     

Cationic polymerization of cyclic olefins

The polymerization and the polymerizabilities of indene, benzofuran, and 1,2-dihydronaphthalene are discussed from the point of view of ring strain, ring stabilization, and steric hindrance in the transition state. Monomer reactivities of these olefins were estimated from copolymerization with styrene and from the rate of addition of iodine bromide in acetic acid. Rates and degrees of polymerization are compared with monomer reactivities and resonance energies of indene, 1,2-dihydronaphthalene, and benzofuran as a measure of ring strain and stabilization. It is found that indence is 1.5–2.0 times more reactive than styrene. This high reactivity of indene is attributed to the ring strain in the monomer state and to the low amount of steric hindrance in the transition state of the coplanar five-membered cyclic olefin. 1,2-Dihydronaphthalene is strained and therefore reactive, but propagation to higher molecular weight products is impeded due to the steric hindrance. The reactivity of benzofuran is decreased by conjugative stabilization of C?C double bonds at the reaction site.     

Reaction of poly(vinyl chloride) with magnesium and grignard reagents

Reaction of poly(vinyl chloride) with magnesium under various conditions was attempted, but poly(vinyl chloride) did not react with magnesium. The reactions of poly(vinyl chloride) with benzylmagnesium chloride and allylmagnesium chloride as Grignard reagents were carried out in tetrahydrofuran at reflux temperature. It was found that the chlorine atoms in the poly(vinyl chloride) were replaced by benzyl and allyl groups by the coupling reaction, and a small amount of Grignard reagent of poly(vinyl chloride) was formed by the magnesium–halogen exchange reaction. The extent of the substitution increased with increasing reaction time and concentration of the Grignard reagent.