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21.
Chanmahasathien W Li Y Satake M Oshima Y Ishibashi M Ruangrungsi N Ohizumi Y 《Chemical & pharmaceutical bulletin》2003,51(11):1332-1334
A new prenylated xanthone, 1,3,5,6-tetrahydroxy-4,7,8-tri(3-methyl-2-butenyl)xanthone (1), was isolated from the wood of Garcinia xanthochymus together with a known xanthone, garciniaxanthone E (2). Their structures were determined by spectroscopic analysis. Compounds 1 (3 microM) and 2 (10 microM) elicited marked enhancement of nerve growth factor-mediated neurite outgrowth in PC12D cells. 相似文献
22.
Novel synthesis of heterocyclic spirans by tandem cycloaddition to sulfur-containing heterocumulenes
Yoshiki Ohshiro Hitoshi Nanimoto Hiroyuki Tanaka Mitsuo Komatsu Toshio Agawa Noritake Yasuoka Yasushi Kai Nobutami Kasai 《Tetrahedron letters》1985,26(25):3015-3018
Novel Ni(C0)4-promoted tandem cycloadditions of diphenylcyclo- propenone to isothiocyanates and to CS2 were found to provide new heterocyclic spirans, pyrroline-2-one-5-spiro-5′-thiolene-4′-ones and a thiolene-2-one-5-spiro-5′-thiolene-4′-one, respectively, in moderate yields. 相似文献
23.
Unesterified carbamoyl- and thiocarbamoyl-phosphonic acids were prepared in high yields by the reaction of tris(trimethylsilyl) phosphite with isocyanates and isothiocyanates followed by treatment of the 1:1 carbonyl adducts with aniline-containing methanol. 相似文献
24.
Homogeneous palladium catalyst suppressing Pd black formation in air oxidation of alcohols 总被引:1,自引:0,他引:1
Iwasawa T Tokunaga M Obora Y Tsuji Y 《Journal of the American Chemical Society》2004,126(21):6554-6555
In homogeneous catalyst systems, there is the persistent problem that metal aggregation and precipitation cause catalyst decomposition and considerable loss of catalytic activity. Pd black formation is a typical example. Pd catalysts are known to easily aggregate and form Pd black, although they realize a wide variety of useful reactions in organic synthesis. In order to overcome this intrinsic problem of homogeneous Pd catalysis, we explored a new class of Pd catalyst by adopting aerobic oxidation of alcohols as a probe reaction. Herein we report a new catalyst system that suppresses the Pd black formation even under air and with a high substrate to catalyst molar ratio (S/C: more than 1000) in oxidation of alcohols. The novel pyridine derivatives having a 2,3,4,5-tetraphenylphenyl substituent and its higher dendritic unit at the 3-position of the pyridine ring were found to be excellent ligands with Pd(OAc)2 in the palladium-catalyzed air (balloon) oxidation of alcohols in toluene at 80 degrees C. Comparison with structurally related pyridine ligands revealed that introduction of the 2,3,4,5-tetraphenylphenyl substituent at the 3-position of pyridine ring effectively suppresses the Pd black formation, maintaining the catalytic activity for a long time to give aldehydes or ketones as products in high yields. 相似文献
25.
Toshinobu Suzuki Yasushi Nagae Keiryo Mitsuhashi 《Journal of heterocyclic chemistry》1986,23(5):1419-1421
Novel synthesis of the title compounds by the facile cyclization between 2,3-dichloro-5,6-dicyanopyrazine and various 2-aminopyridines under relatively mild conditions is described. The reactivity depended on the basicity of 2-aminopyridines. 相似文献
26.
Yasushi Mizobe Reiko Ono Yasuzo Uchida Masanobu Hidai Meguru Tezuka Suehiro Moue Atsuhiko Tsuchiya 《Journal of organometallic chemistry》1980,204(3):377-385
Diazoalkane complexes of type [MF(NNCRR′)(dpe)2][BF4] (M = Mo or W; dpe = Ph2PCH2CH2PPh2), which are easily derived from bis(dinitrogen) complexes [M(N2)2(dpe)2], undergo consecutive one- and two-electron oxidations and reductions under voltammetric conditions at a platinum electrode. The ESR spectra of the species generated by the controlled potential electrolysis show that primary oxidation occurred on the metal atom (M = Mo) and reduction on the two nitrogen atoms in the diazoalkane ligands (M = Mo or W). 相似文献
27.
A new N-unprotected phosphoramidite method called the "proton-block" approach was developed for the chemical synthesis of oligodeoxynucleotides based on the hitherto simplest and rational principle of acid-base reactions. This concept involves protection of the nucleobases of deoxycytidine and deoxyadenosine with "protons" to convert them to unreactive protonated bases during condensation by use of promoters having pK(a) values lower than 2.8. This strategy was applied to the synthesis of d[CpT] and d[ApT] to check the side reactions associated with the base residues. In this "proton-block" method, 5-nitrobenzimidazolium triflate (NBT) was found to be the best promoter, and THF was superior to CH(3)CN as the solvent so that the concomitant detritylation due to the inherent acidity of the promoter could be greatly suppressed. Application of this strategy to the solid-phase synthesis gave d[CpT], d[ApT], d[ApA], d[CpC], and d[GpT] as almost single peaks in HPLC analysis. Similarly, d[ApApApT] and d[CpCpCpT] were successfully synthesized without significant side reactions. Finally, d[CpCpCpCpCpCpT] and d[ApApApApApApT] were obtained as the main products. In the case of a longer oligomer, d[CpApGpTpCpApGpTpCpApGpT], a mixed solvent of CH(3)CN-N-methylpyrrolidone (1:1, v/v) was superior to THF so that the desired oligodeoxynucleotide could be isolated in a satisfactory yield. These results suggest that DNA synthesis can be carried out simply by using the protonated bases at the oligomer level not only without base protection but also without the capping reaction and the posttreatment of branched chains with MeOH-benzimidazolium triflate that previously was requisite. It is concluded that most of the reactions and solvent effects involved in this strategy can be explained in terms of simple acid-base reactions. Some problems associated with the previous posttreatment are also discussed with our own results. 相似文献
28.
Intramolecular alkene-carbonyl coupling reaction of N-benzyl-N-(o-alkenylaryl)carbamate derivative derived from o-aminostyrene, o-(aminomethyl)styrene and o-aminoallylbenzene smoothly proceeded by treating with zirconocene-butene complex to give the corresponding lactam derivative. 相似文献
29.
Sorption processes of methylene blue in a single silica gel microparticle in an aqueous solution was kinetically analyzed by a new technique combined with the microcapillary injection/manipulation and microabsorptiometry of the single particle. The observed sorption rates were analyzed in terms of the solute concentration in water and the particle size. The sorption processes were governed by diffusion of the solute in the particle. Copyright 2000 Academic Press. 相似文献
30.
Masao Tomoi Satoru Ishigaki Yasushi Arita Hiroshi Kakiuchi 《Journal of polymer science. Part A, Polymer chemistry》1988,26(8):2251-2261
Polystyrene-bound 4-(1-pyrrolidino)pyridine moieties were prepared by the reaction of chloromethylated polystyrene resins with pyrrolidinopyridine derivatives containing hydroxyl groups. The supported amines were effective catalysts for acylations of tert-alcohols or enols, acylrearrangements, and diester synthesis from epoxides and anhydrides. Some of the low ring-substituted (8–15%) catalysts exhibited high activity comparable to that of 4-(N,N-dimethylamino)pyridine, though the activity was a little lower than that of 4-(1-pyrrolidino)pyridine. The recovered catalysts can be re-used, except for acyl rearrangements, without significant decrease in activity. 相似文献