Ionic polymers and oligomers with expanded π-conjugation system derived from through-space interaction in piperazinium ring

Reactions of N-(2,4-dinitrophenyl)-4-arylpyridinium chlorides (aryl (Ar) = phenyl and 4-pyridyl) with piperazines caused the ring opening of the pyridinium ring and yielded polymers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units [N(CH(R)CH₂)₂N⁺(Cl⁻)CHCHC(Ar)CHCH, RH, Me, and phenyl]. However, the same reactions occurring in the presence of piperidine yielded oligomers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units having piperidine and/or piperazine rings at both ends. ¹H NMR spectra suggested that π-electrons of the penta-2,4-dienylideneammonium group of the polymers and the oligomers were delocalized. UV-vis measurements revealed that the π-conjugation system expanded along the polymer and oligomer chains due to the orbital interaction between electrons on the two nitrogen atoms of the piperazinium ring. Conversion of the piperazinium ring from the boat form to the chair form caused decrease in the π-conjugation length. The rate constants of the conversion of the oligomers depended on their chain lengths. The surface of pellets that were molded from the polymers and oligomers exhibited metallic luster. These polymers and oligomers underwent electrochemical oxidation in solution.     

Reactivity of the ester group attached isoxazoline, benzisoxazole, and isoxazole: a facial preparation of 3-acyl-substituted these heterocycles

A facile preparation of 3-acyl-substituted isoxazolines, benzisoxazoles, and isoxazoles from the corresponding 3-carboxylate esters is described. The process, involving reaction of the ester derivative of 3-carboxylic acid substituted heterocycles with Grignard or alkynyl lithium reagents, leads to direct generation of the corresponding 3-acyl heterocycle. The presence of α-imino ester moieties in the heterocyclic substrates for the reactions is thought to be a key feature governing the nature of these transformations. The synthetic utility of the new methodology is demonstrated by its application in a two-step route for the preparation of novel linked bis-heterocycles.     

Synthesis of 7‐acetyloxy‐3,7‐dimethy1‐7,8‐dihydro‐6H‐isochromene‐6,8‐dione and its analogues

7‐Alkanoyloxy‐3,7‐dimefhyl‐7,8‐dihydro‐6H‐isochromene‐6,8‐diones 12‐15 were synthesized in 69‐16% yields from the reaction of 2,4‐dihydroxy‐3‐methyl‐6‐(2‐oxopropyl)benzaldehyde 11 with p‐toluenesulfonic acid in various carboxylic acids such as acetic acid, propionic acid, butyric acid and heptanoic acid followed by oxidation with lead tetraacetate. On the other hand, (±)‐daldinin A 5 (oleate) was not obtained using oleic acid as a medium. In the cases of heptanoic acid and oleic acid, esters 16 and 17 were produced in 23 and 9% yields, respectively. 6,8‐Dihydroxy‐3,7‐dimethyl‐2‐benzopyrylium p‐toluenesulfonate 31 is considered as the intermediate for the production of 12‐15. Overall yields of isochromenes 12‐15 were 26‐6% starting from 2‐methylresorcinol for seven steps.     

Crystal structure of methyl endo-8-cyano-exo-8-methyl-3-oxo-2-oxabicyclo[2.2.2]oct-5-ene-6-carboxylate.

A photochemical cycloaddition reaction of methyl 2-pyrone-5-carboxylate with methacrylonitrile mainly gave a [4 + 2] cycloadduct, assigned as methyl endo-8-cyano-exo-8-methyl-3-oxo-2-oxabicyclo[2.2.2]oct-5-ene-6-carboxylate, whose structure was determined by an X-ray diffraction study. The formation of the cycloadduct was reasonably explained by considering a biradical intermediate having a less steric hindrance between the methoxycarbonyl group and the cyano group.     

Cepaic acid, a novel yellow xanthylium pigment from the dried outer scales of the yellow onion Allium cepa

Cepaic acid was isolated as a novel xanthylium yellow pigment from the dried outer scales of the yellow onion Allium cepa Linne. Its structure was elucidated on the basis of ESI-MS and 2D NMR spectroscopy as a 9-carboxy-1,3,6,8-tetrahydroxyxanthylium, which suggests that cepaic acid and other yellow pigments in the dried outer skin of onion were formed by the nucleophilic reaction of phloroglucinol derived from quercetin, a flavonol in onion scales, by autoxidation to glyoxylic acid. To our knowledge, this is the first report of such a pigment in yellow onion.     

Preparation of poly(1,4-phenylene)s by electro-oxidative polymerization

The effect of substituents on the electropolymerization of benzene derivatives and the redox properrties of the corresponding polymers were determined using Brown's substituent constants (σ⁺). Electron-donating groups lower the oxidation potential by which increase in the current efficiency was observed. However, stabilization of the produced cation radicals by the electron-donating groups resulted in a decrease in the polymerization efficiency. The appropriate values of σ⁺ for the efficient polymerization ranged near ?1.5.     

Carbazole Dendrimers as Solution‐Processable Thermally Activated Delayed‐Fluorescence Materials

Recently, thermally activated delayed fluorescence (TADF) materials have received increasing attention as effective emitters for organic light‐emitting diodes (OLEDs). However, most of them are usually employed as dopants in a host material. In this report, carbazole dendrimers with a triphenyl‐s‐triazine core are reported, which are the first solution‐processable, non‐doped, high‐molecular‐weight TADF materials. The dendrimers were obtained by a new and facile synthetic route using the tert‐butyldimethylsilyl moiety as a protecting group. All dendrimers showed TADF in toluene. Measurements of the temperature‐dependent luminescence lifetime revealed that spin‐coated neat films also showed TADF with moderate quantum yields. OLED devices incorporating these dendrimers as spin‐coated emitting layers gave external quantum efficiencies of up to a 3.4 %, which suggests that this device is harvesting triplet excitons. This result indicates that carbazole dendrimers with attached acceptors are potential TADF materials owing to their polarized electronic structure (with HOMO–LUMO separation).     

Synthesis of Disaccharide Nucleosides by the O‐Glycosylation of Natural Nucleosides with Thioglycoside Donors

Disaccharide nucleosides constitute an important group of naturally‐occurring sugar derivatives. In this study, we report on the synthesis of disaccharide nucleosides by the direct O‐glycosylation of nucleoside acceptors, such as adenosine, guanosine, thymidine, and cytidine, with glycosyl donors. Among the glycosyl donors tested, thioglycosides were found to give the corresponding disaccharide nucleosides in moderate to high chemical yields with the above nucleoside acceptors using p‐toluenesulfenyl chloride (TolSCl) and silver triflate (AgOTf) as promoters. The interaction of these promoters with nucleoside acceptors was examined by ¹H NMR spectroscopic experiments.