共查询到20条相似文献,搜索用时 160 毫秒
1.
Deprotonation/methylation reactions have been carried out on a series of substituted 2-sulfolenes and 3-sulfolenes. For 2-sulfolenes, both allylic and vinylic deprotonation reactions occur to give, after treatment with methyl iodide, 2-methylated 3-sulfolenes and 2-methylated 2-sulfolenes. These products are useful intermediates because substituted 3-sulfolenes are precursors to substituted butadienes and 2-alkylated 2-sulfolenes are precursors to β-functionalized trans olefins. 相似文献
2.
Fragmentations of the title precursors in polar solvents proceed via similar ion pairs to mixtures of exo-2-chloro-5-norbornene and 3-nortricyclyl chloride. The stereochemical course of the conversions is mainly determined by least motion chloride return in ion pair intermediates. 相似文献
3.
Biosynthesis of the polyketide, dehydrocurvularin 1, by Alternaria cinerariae was examined by incorporation experiments with N-acetylcysteamine (NAC) thiolesters of potential labeled di-, tri-, tetra-, and pentaketide assembly intermediates, 5–10. The results show that diketide and ,β-unsaturated tetraketide precursors can be utilized intact, whereas a saturated tetraketide can not, thereby suggesting that 1 is the initial PKS product. Curvularin 2 and 1 could not be interconverted by A. cinerariae, but 8-hydroxycurvularin 3 and 1 are transformed into each other by component(s) in the fermentation media. 相似文献
4.
An efficient method for the stereoselective synthesis of l-ribose was accomplished starting from commercially inexpensive d-fructose. The intermediates in the process can serve as versatile precursors for the preparation of l-nucleoside analogues. 相似文献
5.
Daniel F. Persico Richard J. Lagow 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):233-242
Linear polyester precursors provide a convenient low cost synthesis for flurocarbon surfactants, diacids, diesters, and intermediates. A reaction scheme starting with hydrocarbon linear polysters followed by conversion of the ester to a perfluoro ester by direct fluorination and subsequent treatment with nonstoichiometric amount of sulfur tetrafluoride produce upon hydrolysis of ester units remaining in the polymer, low molecular weight perfluropolyether diacids. Alternatively, this technique can be altered slightly to produce diesters and other functional perfluorocarbon intermediates. 相似文献
6.
Yong Guo 《Journal of fluorine chemistry》2007,128(10):1280-1285
A review of difluoromethylene compounds as precursors to carbonyl compounds. Many ketones, carboxylic acids, esters, amides and carbonates, especially trifluoroalanine dipeptides, can be easily achieved due to the reactivity of difluoromethylene compounds or generated through the reactive difluoromethylene intermediates. 相似文献
7.
D. Logvinovich A. Brger M. Dbeli S.G. Ebbinghaus A. Reller A. Weidenkaff 《Progress in Solid State Chemistry》2007,35(2-4):281-290
Oxynitrides with the general formula La1−xCaxTiO2+xN1−x (x = 0, 0.3, 0.5, 0.7, 1.0) were synthesized by thermal ammonolysis of oxide precursors produced with a soft chemistry method. The crystallographic structure, optical properties and the thermal stability of the compounds were studied with X-ray diffraction, UV–vis spectroscopy and thermal analysis.
All materials crystallize in perovskite-type pseudo-cubic unit cell. It was found that the lattice parameter decreases with increasing Ca content, while the optical band gap width increases with increasing x. Thermal reoxidation studies of the synthesized materials reveal the formation of nitrogen rich intermediates. The decomposition rate of the intermediates was correlated with the structure of the final products. TEM studies show a preferred insertion direction of the nitrogen into the crystal lattice of the starting oxides. Ammonolysis with flux significantly changed the microstructure of the obtained oxynitrides. 相似文献
8.
Silver‐Catalyzed Amidiniumation of Alkynes: Isolation of a Silver Intermediate,Synthesis of Enamine Amido Carbene Precursors,and an Unprecedented Umpolung of Propiolamide
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shichang Lv Jiwei Wang Caiyun Zhang Dr. Sheng Xu Prof. Dr. Min Shi Dr. Jun Zhang 《Angewandte Chemie (International ed. in English)》2015,54(49):14941-14946
A silver‐catalyzed amidiniumation of N‐propiolic formamidines for the synthesis of novel enamine amido carbene precursors is reported. Isolation of a first silver intermediate in silver‐catalyzed amidiniumation of alkynes and other organogold intermediates supports our proposed mechanisms. Several control experiments reveal the unexpected effects of both HOTf and substrate substituents on the choice of either a π or σ,π silver activation mode and the cyclization fashion. Bis(hydroxyimidazol)ium salts were obtained through an unprecedented umpolung of propiolamides. The byproduct Ag2O as either an oxidant or silver source promotes the syntheses of N‐heterocyclic carbene (NHC) precursors or Ag/NHC complexes. 相似文献
9.
Shichang Lv Jiwei Wang Caiyun Zhang Sheng Xu Min Shi Jun Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(49):15154-15159
A silver‐catalyzed amidiniumation of N‐propiolic formamidines for the synthesis of novel enamine amido carbene precursors is reported. Isolation of a first silver intermediate in silver‐catalyzed amidiniumation of alkynes and other organogold intermediates supports our proposed mechanisms. Several control experiments reveal the unexpected effects of both HOTf and substrate substituents on the choice of either a π or σ,π silver activation mode and the cyclization fashion. Bis(hydroxyimidazol)ium salts were obtained through an unprecedented umpolung of propiolamides. The byproduct Ag2O as either an oxidant or silver source promotes the syntheses of N‐heterocyclic carbene (NHC) precursors or Ag/NHC complexes. 相似文献
10.
Ioannis K. Stamos 《Tetrahedron letters》1985,26(4):477-480
Pummerer intermediates generated from precursors (3), (4) and (5) reacted mildly with aromatic compounds in the presence of Lewis acids to give the corresponding sulfides which in turn desulfurized to arylmethylene ketones, arylacetoesters, and arylacetonitriles. 相似文献
11.
Sessler JL Aguilar A Sanchez-Garcia D Seidel D Köhler T Arp F Lynch VM 《Organic letters》2005,7(10):1887-1890
alpha,alpha-Linked oligopyrroles are attractive precursors for both expanded porphyrin and conducting polymer chemistry. We demonstrate facile methods for synthesizing quater-, penta-, and sexipyrroles from more readily available bi- and terpyrrole intermediates. These products demonstrate stability in their brightly colored oxidized forms, while reduction using borohydride reagents gives the corresponding all-pyrrole oligomers, which oxidize readily in air. The oxidized quater- and sexipyrroles were characterized by single-crystal X-ray diffraction analysis. 相似文献
12.
Milhomme O John C Djedaïni-Pilard F Grandjean C 《The Journal of organic chemistry》2011,76(15):5985-5998
Anthrose is the upstream terminal unit of the tetrasaccharide side chain from a major glycoprotein of Bacillus anthracis exosporium and is part of important antigenic determinants. A novel entry to anthrose-containing antigens and precursors is described. The synthetic route, starting from D(+)-fucose, makes use of intermediates featuring a cyclic sulfite or sulfate function which serves successively as a protecting and a leaving group. 相似文献
13.
Dr. Zhongrui Chen Dr. Rose Haddoub Jérôme Mahé Dr. Gabriel Marchand Prof. Denis Jacquemin Dr. Judicaelle Andeme Edzang Dr. Gabriel Canard Dr. Daniel Ferry Dr. Olivier Grauby Alain Ranguis Dr. Olivier Siri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17820-17832
Pre‐ and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N‐substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N‐substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N‐substituents, the formation of supramolecular ribbon‐like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments. 相似文献
14.
Yumiko Suzuki Naoto Iwata Kohei Dobashi Ryo Takashima Sundaram Arulmozhiraja Erika Ishitsubo Naoya Matsuo Hiroaki Tokiwa 《Tetrahedron》2018,74(3):392-400
A combined experimental and computational study on the key intermediates of NHC-catalyzed acylation reaction, Breslow intermediates (BIs), has been conducted in order to achieve a direct nucleophilic alkanoylation of N-heterocycles. Various BI precursors are alternatively prepared and used in the reaction with 4-chloroquinazoline. The present study reveals that the intermediates having benzimidazole moiety serve as acylating agents for the introduction of straight-chain alkanoyl groups. Natural bond orbital analysis indicates that the reactivity of intermediates partly correlates to the occupancy of the πC-C bonds of the hydroxyl enamine moieties. The putative rate-determining step of the acylation reaction has been theoretically investigated. Several new 4-alkanoylquinazolines are synthesized using the BI precursors. 相似文献
15.
A novel strategy has been developed to generate a diverse array of privileged scaffolds from readily available tetrahydropyridine precursors that may be prepared by a multicomponent assembly process followed by a ring-closing metathesis. The functionality embedded in these key intermediates enables their facile elaboration into more complex structures of biological relevance by a variety of ring-forming processes and refunctionalizations. 相似文献
16.
《合成通讯》2013,43(12):1675-1680
Abstract A series of ω‐bromo‐2(S)‐methyl acids has been synthesized as precursors of novel arginine (Arg), lysine (Lys), and mercapto analogues. These intermediates contain α‐methyl groups and are designed to mask the N‐terminal amine when incorporated in pharmaceutically relevant peptides. 相似文献
17.
Fustero S Cuñat AC Flores S Báez C Oliver J Cynamon M Gütschow M Mertens MD Delgado O Tresadern G Trabanco AA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(52):14772-14784
The preparation of novel fluorinated allylamines and their use as key fragments for the stereoselective synthesis of hydroxyethyl secondary amine (HEA)-type peptidomimetics is described. Our strategy employs chiral sulfinyl imines as synthesis intermediates, by treatment of hemiaminal precursors with two equivalents of vinylmagnesium bromide. The subsequent oxidation of the allylic amines to the corresponding epoxides was achieved by treatment with methyl(trifluoromethyl)dioxirane. Finally, epoxide ring opening with a range of nitrogen nucleophiles provided a library of HEA-derived peptidomimetics with a phenyldifluoromethylene moiety. The biological evaluation of these derivatives revealed compounds with remarkable BACE1 inhibitory activity. Docking studies revealed the influence of the fluorine atoms in the binding mode of the synthesized ligands. Furthermore, the biological evaluation of our final products and synthesis intermediates led to the discovery of compounds with antimicrobial activity against Mycobacterium and Nocardia species. 相似文献
18.
o-bromoacetophenone derivatives as new versatile aryne precursors are induced to selectively eliminate the CArBr and CArC(Ac) bonds in the help of t-BuOK. Furthermore, the active aryne intermediates are successfully applied in a substantial set of reactions including N-arylation and copper-catalyzed coupling with various terminal alkynes. It is important to note that the generation of benzyne intermediate is demonstrated through cycloadditon reaction experiment with furan. 相似文献
19.
Wen‐Hsin Lin Chih‐Chiang Tu Shyi‐Long Lee 《International journal of quantum chemistry》2005,103(4):355-368
The ring‐collapse mechanism of C24 (D6d) has been analyzed using semiempirical AM1 and B3LYP/cc‐pVDZ methods. Based on the ring‐stacking/circumscribing model, two precursors are selected. Transition states and intermediates are located and energetics are computed. Before the stacking begins, the precursor and belt reach a suitable relative orientation accompanied by the release of a large amount of energy. It is observed that the reactions between the precursors and the belts are essentially endoergic in nature, whereas the reactions between the stable intermediates and the final belts are exoergic. The deformation energies (DE) and the bond lengths R of the precursors have been computed. The DE values suggest that there is a chance of the cleavage of the bicyclic precursors as the growth process proceeds toward the cage formation. In contrast, the monocyclic precursor is found to have lower deformation energies than the bicyclic precursor. Analysis of average bond length at different cages shows that a large window is formed and the system appears to follow a cascade‐type bond formation. Comparisons are made to our previous results on C28 growth. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
20.
Dihydropyrimidines (DHPM) with a fused tetrazole ring have been synthesized via a smooth and efficient three-step protocol involving N,S-dimethylated and 2-hydrazinyl-dihydropyrimidine intermediates, respectively. The described protocol is applicable to electron rich and electron poor DHPM precursors as well. The insertion of tetrazole ring in monastrol type dihydropyrimidines makes it interesting for pharmacological investigations. 相似文献