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141.
[reaction: see text] Prenyl (3-methylbut-2-enyl) ester is catalytically cleaved by TMS triflate affording carboxylic acid and isoprene in high yield under mild conditions with high chemoselectivity without causing epimerization of the neighboring chiral center. 相似文献
142.
Chatterjee B Noveron JC Resendiz MJ Liu J Yamamoto T Parker D Cinke M Nguyen CV Arif AM Stang PJ 《Journal of the American Chemical Society》2004,126(34):10645-10656
The syntheses, structures, and N2 adsorption properties of six new supramolecular metallacycles are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)2, where M = Pt(II) and Pd(II), and cis-(Me3P)2Pt(OTf)2 to form flexible supramolecular metallacycles 5-10 in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm3/g STP of N2 at 77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5 is flexible, a property which was transferred from the linker to the supramolecular structure in the solid state. 相似文献
143.
Jyunichi Koyanagi Katsumi Yamamoto Kouji Nakayama Akira Tanaka 《Journal of heterocyclic chemistry》1997,34(2):407-412
4,9-Dimethoxynaphtho[2,3-b]furan 9 was obtained in 91% yield via the reductive methylation of naphtho[2,3-b]furan-4,9-dione 2 . After treatment of 9 with butyllithium, the mixture was allowed to react with N,N-dimethylacetamide, followed by oxidization with cerium(IV) diammonium nitrate to give 2-acetylnaphtho[2,3-b]furan-4,9-dione 1 . 2-Formylnaphtho[2,3-b]furan-4,9-dione 13 and 2-trimethylsilyl-naphtho[2,3-b]furan-4,9-dione 14 were also obtained from 9 by a similar method. The halodesilylations of 14 easily gave 2-iodonaphtho[2,3-b]furan-4,9-dione 16 , 2-bromonaphtho[2,3-b]furan-4,9-dione 17 , and 2-chloronaphtho[2,3-b]furan-4,9-dione 18 in 82%, and 93% and 83% yield, respectively. Furthermore, the nitrodesilylation of 14 gave 2-nitronaphtho[2,3-b]furan-4,9-dione 3 in 77% yield. 相似文献
144.
Masataka Hiraide Kennich Ishikawa Zuo Sheng Chen Hiroshi Kawaguchi 《Mikrochimica acta》1994,117(1-2):7-13
Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater. 相似文献
145.
Cao B Wakahara T Tsuchiya T Kondo M Maeda Y Aminur Rahman GM Akasaka T Kobayashi K Nagase S Yamamoto K 《Journal of the American Chemical Society》2004,126(30):9164-9165
A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5). 相似文献
146.
147.
148.
Vitamin E glycosides were synthesized and enzymatic hydrolysis was examined for use as potential pro-drugs, however, the glycoside bond was found to be stable. On the other hand, among the glycosides synthesized, dl-alpha-tocopherylglucoside (6b) and dl-alpha-tocopherylmannoside (6c) showed strong inhibitory action on histamine release from mast cells. In addition, 6c also showed a suppressive action on IgE antibody formation. Thus, tocopheryl glycoside showed new properties compared to tocopherol (vitamin E). In particular, 6c was shown to be a novel lead compound with excellent manifold anti-allergic activity and anti-inflammatory activity. 相似文献
149.
In this letter, we report synthesis of branched polysaccharide 2 by glycosylation of glucal-type monomer 1 with two free hydroxy groups at position 3 and 4. Monomer 1 polymerized with N-halosuccinimide promoter in acetonitrile solvent at room temperature--50 degrees C. The product was isolated as a petroleum ether insoluble fraction. The structure was determined by 1H and 13C NMR spectra as well as elemental analysis to be a polysaccharide consisting of 2-halo-2-deoxy-alpha-D-mannoside units, indicating that the polymerization proceeded via stereoregular glycosylation manner. The molecular weights determined by GPC with DMF were 3,300-4,000. The degree of branching was estimated by the NMR data of the product from the reaction of 2 with 3,5-dinitrobenzoyl chloride. 相似文献
150.
Phenotyping of erythrocyte acid phosphatase (EAP) and esterase D (ESD) by cellulose acetate membrane isoelectric focusing (CAM-IEF) under a nonequilibrium condition is described. In an attempt to improve the method of CAM-IEF, we shortened the electrode distance to provide a higher field strength at a given (low) voltage. Various carrier ampholytes for EAP typing and various chemical separators for ESD typing were also tested. Good separations were obtained after 30 min IEF for EAP typing and 25 min for ESD typing. When applied to blood stains and stored for various periods at room temperature, the stains up to 8 months old could still be phenotyped for EAP and those up to 4 weeks old for ESD. CAM-IEF is suitable for routine forensic work of EAP and ESD phenotyping. 相似文献