Tetrahedron Letters

Editorial board ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17
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Graphical Contents List ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17
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1,3-Diyne chemistry: synthesis and derivations ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Wei Shi , Aiwen Lei Conjugated diynes have attracted more and more attention not only for their unique rod like structures and wide existence in nature product, but also the abundant properties and derivations of them. Although oxidative dimerization of alkynes or Cadiot–Chodkiewicz reactions were the main pathway and have achieved great success in the synthesis of diynes, oxidative cross coupling, FBW rearrangement as well as diyne metathesis emerged rapidly recently. Moreover, diynes could be precursors of basic heterocycles, which represented an emerging research area. This Letter will cover the recent progresses in the synthesis and further derivations of diynes. Graphical abstract image
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Recent progress in the chemistry and chemical biology of microbial signaling molecules: quorum-sensing pheromones and microbial hormones ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Arata Yajima Communication among microorganisms is mediated by secretion and detection of microbial signaling molecules such as quorum-sensing pheromones and microbial hormones. The molecules elicit the regulation of important genes necessary for microbial survival and often play important roles in interspecies or even inter-kingdom communication. Recent progress in the study of the signaling molecules has enabled us to eavesdrop on microbial conversations to gain insight on their intercellular communication system. This review summarizes the recent advances in the chemistry and chemical biology of these important microbial signaling molecules: acyl-homoserine lactones (AHLs), AI-2, CAI-1 related α-hydroxy ketones (AHKs), ComX pheromones, diffusible signal factors (DSFs), diffusible extracellular factor (DF), and Phytophthora mating hormones. Graphical abstract image
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Chemoselective reductions and iodinations using titanium tetraiodide ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Iwao Hachiya , Makoto Shimizu Titanium(IV) halides are extensively used in carboncarbon bond forming reactions as a Lewis acid and low valent titanium halides promote reductive coupling reactions of carbonyl compounds. In most of these reactions, ligands of titanium halides are chloride or bromide. On the other hand, titanium(IV) tetraiodide had been rarely used in organic synthesis until the late 1990s. Since 2000 several useful synthetic reactions have been developed utilizing a moderate Lewis acidity, reducing and iodination abilities of titanium(IV) tetraiodide. This digest summarizes examples of chemoselective reductions and iodinations using titanium(IV) tetraiodide (TiI4). Graphical abstract image
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Marine bacterial inhibitors from the sponge-derived fungus Aspergillus sp. ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Yaming Zhou , Abdessamad Debbab , Victor Wray , WenHan Lin , Barbara Schulz , Rozenn Trepos , Claire Pile , Claire Hellio , Peter Proksch , Amal H. Aly Chromatographic separation of a crude extract obtained from the fungus Aspergillus sp., isolated from the Mediterranean sponge Tethya aurantium, yielded a new tryptophan derived alkaloid, 3-((1-hydroxy-3-(2-methylbut-3-en-2-yl)-2-oxoindolin-3-yl)methyl)-1-methyl-3,4-dihydrobenzo[e][1,4]diazepine-2,5-dione (1), and a new meroterpenoid, austalide R (2), together with three known compounds (3–5). The structures of the new compounds were unambiguously elucidated on the basis of extensive one and two-dimensional NMR (1H, 13C, COSY, HMBC, and ROESY) and mass spectral analysis. Interestingly, the compounds exhibited antibacterial activity when tested against a panel of marine bacteria, with 1 selectively inhibiting Vibrio species and 2 showing a broad spectrum of activity. In contrast, no significant activity was observed against terrestrial bacterial strains and the murine cancer cell line L5178Y. Graphical abstract image
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Metal-free diastereoselective synthesis of diaza-bicyclo[3.2.0]heptan-7-one and its transformation to functionalized proline esters ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Yogesh Kumar , Bilash Kuila , Dinesh Mahajan , Prabhpreet Singh , Balaram Mohapatra , Gaurav Bhargava A metal-free diastereoselective synthesis of novel 4-halo-3,6-di-aryl-2,6-diaza-bicyclo[3.2.0]heptan-7-one by intramolecular endo-trig haloamination of 3-amino-2-azetidinone is reported. The amidiolytic ring opening of diaza-bicyclo[3.2.0]heptan-7-one with sodium methoxide provides an easy access to previously unknown 4-halo-3-aryl amino-pyrrolidine-2-carboxylic acid methyl esters in good yields. Graphical abstract image
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Microwave-assisted parallel synthesis of benzofuran-2-carboxamide derivatives bearing anti-inflammatory, analgesic and antipyretic agents ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Yong-Sheng Xie , Deepak Kumar , V.D. Vijaykumar Bodduri , P. Srivastava Tarani , Bao-Xiang Zhao , Jun-Ying Miao , Kiwan Jang , Dong-Soo Shin A series of benzofuran-2-carboxamides of biological and medicinal significance were synthesized by a microwave-assisted one-pot parallel approach via O-alkylation/Knoevenagel condensation. All the compounds were characterized and assayed for their in vivo anti-inflammatory, analgesic and antipyretic activities. The activity data of all compounds were listed and discussed in detail, among which some derivatives exhibited potent activities of particular interest. Graphical abstract image
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[2+2] photodimerization of 1-aryl-4-pyridylbutadienes through cation–π interactions ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Shinji Yamada , Yuka Azuma , Kanae Aya Irradiation of 1-aryl-4-pyridylbutadienes in the presence of 1equiv of HCl produced syn and anti head-to-tail dimers, among a number of possible dimers, whereas irradiation in the absence of HCl gave a complex mixture. This indicated that the acid serves as a catalyst for the regio- and stereoselective [2+2] photodimerization of 1-aryl-4-pyridylbutadienes through cation–π interactions between the pyridinium and aromatic rings. The produced synHT dimers underwent Cope rearrangement to produce cyclooctadienes, and they were in equilibrium at a ratio of 85:15 in CDCl3. Graphical abstract image
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Nickel-catalyzed intramolecular addition of vinyl or aryl bromides to ketoamides ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Jun-Qing He , Cheng Chen , Wu-Bin Yu , Ren-Rong Liu , Meng Xu , Yu-Jin Li , Jian-Rong Gao , Yi-Xia Jia A nickel-catalyzed intramolecular addition of vinyl or aryl bromides to ketoamides has been developed. The reactions proceeded efficiently with Ni(bpy)Br2 as a catalyst and zinc powder as reducing agent, affording 3-hydroxypyrrolidinones, 3-hydroxyoxindoles, and dihydroquinolinones as important heterocyclic compounds in good to excellent yields. Graphical abstract image
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The reaction of arynes with münchnones: synthesis of isoindoles and azaisoindoles ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Justin M. Lopchuk , Gordon W. Gribble Arynes derived from silyltriflate precursors undergo a smooth 1,3-dipolar cycloaddition with münchnones to furnish isoindoles and azaisoindoles in moderate to high yields. Modification of the fluoride source, solvent, and temperature allows for the selective generation of either isoindoles or benzanthracenimines, the latter of which serve as precursors to polycyclic aromatic hydrocarbons. Graphical abstract image
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Facile synthesis of Fe@Pd nanowires and their catalytic activity in ligand-free CN bond formation in water ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Mahmoud Nasrollahzadeh , Abbas Azarian , Ali Ehsani , Ali Zahraei This work reports a facile synthesis of Fe@Pd nanowires. Ligand-free cross coupling reactions of arylboronic acids with various amines in aqueous medium proceed in very good to excellent yield with the use of Fe@Pd nanowires. Furthermore, the catalyst could be easily separated from the reaction mixture using a magnet and could be recycled several times without loss of catalytic activity. Graphical abstract image
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Chiral cobalt(II)-salen-catalyzed Michael addition of amines to β-substituted nitroalkenes ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Takumi Kobayashi , Tatsuki Shimura , Yuzuru Kurita , Yoshitaka Katsumata , Satoko Kezuka Optically active cobalt(II) salen complexes were found to be effective Lewis acid catalysts for the enantioselective Michael addition of O-alkylhydroxylamines to nitroalkenes to afford the corresponding N-alkylhydroxyl-1,2-nitroamines in high yields and with good to high enantioselectivities. This study represents the first example of a transition-metal-catalyzed asymmetric Michael addition of amines to nitroalkenes. Graphical abstract image
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Synthesis of (+)-boronolide and (+)-deacetylboronolide using Pd-catalyzed carbonylation and lactonization ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Yuji Kurogome , Yasunao Hattori , Hidefumi Makabe (+)-Boronolide and (+)-deacetylboronolide were synthesized using Pd-catalyzed CO insertion and lactonization as the key step. As to the 13C NMR data of (+)-deacetylboronolide, the assignment at C-6 position should be revised. Graphical abstract image
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Self-aggregation of a synthetic zinc chlorophyll derivative possessing a 131-dicyanomethylene group as a light-harvesting antenna model ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Hitoshi Tamiaki , Masaki Kuno , Michio Kunieda Zinc methyl 3-hydroxymethyl-131-dicyanomethylene-pyropheophorbide-a, one of the bacteriochlorophyll-d analogs, was prepared by modifying chlorophyll-a. The semi-synthetic compound self-aggregated in an aqueous Triton X-100 solution to give large oligomers with red-shifted and broadened electronic absorption bands. The J-aggregates were similar to self-aggregates of bacteriochlorophyll-d molecules in natural light-harvesting antennas of green photosynthetic bacteria. The strongly electron-withdrawing dicyanomethylene group was an alternative functional moiety of the hydrogen-bond accepting 131-oxo group which had been necessary for such self-aggregation. Graphical abstract image
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Diphenylamine end-capped diketopyrrolopyrroles with phenylene–vinylene conjugation extension ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Štěpán Frebort , Martin Vala , Stanislav Luňák Jr. , Jana Honová , Tomáš Mikysek , Zdeněk Eliáš , Antonín Lyčka Two pyrrolo[3,4-c]pyrrole-1,4-diones (diketopyrrolopyrroles, DPP) with 4″-diphenylamino-stilben-4′-yl substituents at the 3- and 3,6-positions of the DPP heterocycle are synthesized. The 1H and 13C NMR spectra of their soluble derivatives, N(2) and N(5)-dialkylated by 2-ethylhexyl bromoacetate, were completely assigned. Soluble DPPs show photovoltaic activity in bulk heterojunction solar cells. Their electrochemistry and absorption and fluorescence spectra were studied. Graphical abstract image
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Glandulaurencianols A–C, brominated diterpenes from the red alga, Laurencia glandulifera and the sea hare, Aplysia punctata ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Maria Kladi , Dimitrios Ntountaniotis , Maria Zervou , Constantinos Vagias , Efstathia Ioannou , Vassilios Roussis Glandulaurencianols A and B were isolated from the organic extract of the red alga, Laurencia glandulifera, collected from the island of Crete in South Greece. Investigation of the mollusk, Aplysia punctata, collected from the coast of Nea Makri, Central Greece, resulted in the isolation of glandulaurencianols A and C. The structures of the new metabolites, as well as their relative configurations, were established on the basis of thorough analyses of their spectroscopic data. Graphical abstract image
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Synthesis of cis-3-arylated cycloalkylamines through palladium-catalyzed methylene sp3 carbon–hydrogen bond activation ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Atsushi Seki , Yoshiaki Takahashi , Toshiaki Miyake Methylene sp3 carbon–hydrogen bond activation of N-picolinoylcycloalkylamines provides a useful method for synthesizing cis-3-arylated cycloalkylamine derivatives. Pd(II) species catalyzed the γ-arylation of N-picolinoylcycloalkylamines with aryl iodides in the presence of silver carbonate to afford cis-3-arylated N-picolinoylalkylamines in up to 87% yield. Hydrolysis of the amide linkage to give the corresponding cis-3-arylated cycloalkylamines was also demonstrated. Graphical abstract image
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Stereoselective synthesis of zooxanthellactone ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Martin Gjerde Jakobsen , Anders Vik , Trond Vidar Hansen The marine polyunsaturated natural product zooxanthellactone was synthesized in six steps and in 11% overall yield from eicosapentaenoic acid. The key synthetic steps were a Sonogashira cross-coupling reaction and a stereoselective semi-reduction. These efforts, together with NMR and optical rotation data, confirmed the reported structure of zooxanthellactone. Graphical abstract image
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Aerobic oxysulfonylation of alkynes in aqueous media: highly selective access to β-keto sulfones ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Atul K. Singh , Ruchi Chawla , Lal Dhar S. Yadav The first application of inexpensive commercially available sulfinate salts to produce β-keto sulfones directly from alkynes via aerobic oxysulfonylation has been developed. It is a highly selective (undesired Glaser–Hay homo-coupling and ATRA process totally suppressed) general method of functionalization of alkynes on water at room temperature involving FeCl3/K2S2O8 catalyzed formation of sulfonyl radicals from sulfinate salts. Graphical abstract image
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Co(I) catalyzed yne–ene–yne [2+2+2] cycloaddition: synthesis of highly strained pentacyclic bis-lactones. A new access to tetraaryl N-hydroxyphthalimides ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Jérôme Michaux , Rémi Poirot , Jacques Einhorn , Bernard Bessières Highly strained pentacyclic bis-lactones can be obtained by an unusual Co(I) catalyzed [2+2+2] cycloaddition of an yne–ene–yne diester substrate. These bis-lactones can be further transformed into tetraaryl N-hydroxyphthalimides which are potential aerobic oxidation organocatalysts. Graphical abstract image
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Regioselective synthesis of piceatannol from resveratrol: catalysis by two-component flavin-dependent monooxygenase HpaBC in whole cells ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Toshiki Furuya , Kuniki Kino Piceatannol, a valuable biologically active stilbene derivative, was efficiently synthesized from resveratrol. Whole-cell catalysis with HpaBC monooxygenase enabled the regioselective hydroxylation of resveratrol to produce 23mM (5.2gL−1) of piceatannol. Graphical abstract image
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Stereoselective synthesis of scyphostatin hydrophilic moiety ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Kazuaki Kuwata , Masashi Suzuki , Yoshikazu Inami , Kengo Hanaya , Takeshi Sugai , Mitsuru Shoji A stereoselective synthesis of scyphostatin hydrophilic moiety was accomplished. Substrate- and reagent-controlled dihydroxylation of tri- and monosubstituted alkenes afforded desired diols, respectively. Chemo- and stereoselective allylation of α-(methoxycarbonyl)cyclohexanone provided allylcyclohexanol. Oxidative cleavage of glycol and subsequent β-elimination of siloxycyclohexanone furnished the desired epoxycyclohexenone. Graphical abstract image
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Catalytic enantioselective C(sp3)H functionalization: intramolecular benzylic [1,5]-hydride shift ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Jie Yu , Nan Li , Dian-Feng Chen , Shi-Wei Luo The catalytic asymmetric [1,5]-hydride transfer/cyclization sequence involving benzylic C(sp3)H bond was established, providing tetrahydronaphthalene derivatives in moderate to high yield with up to 69%ee, by employing the copper complex of side-armed bisoxazoline as chiral catalyst. Graphical abstract image
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Simultaneous deprotection–oxidation of cyclic hemiacetals: a fine ending for a Ueno–Stork ATRC to dichloro-γ-lactones ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Fabrizio Roncaglia , Franco Ghelfi , Fulvia Felluga , Valentina Poppi Recently we found that a copper catalysed Ueno–Stork cyclization can be a very useful means for the expedient synthesis of dichloro-γ-lactones, but, to take advantage of this step, the method still lacks of an efficient and selective follow-up. This Letter describes our progress in that field, unveiling the use of a supported and recyclable Cr(VI) catalyst for the simultaneous deprotection and oxidation of cyclic dichloro hemiacetals. Graphical abstract image
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Two novel norlignans from Gymnotheca chinensis ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Shi-Ji Xiao , Xin-Xiang Lei , Bing Xia , Hong-Ping Xiao , Da-Hai He , Dong-Mei Fang , Hua-Yi Qi , Fang Chen , Li-Sheng Ding , Yan Zhou Two novel norlignans, gymnothedelignans A and B were isolated from the whole plants of Gymnotheca chinensis. These norlignans possess a rare 2/5 epoxy benzocycloheptanone skeleton. Their structures were established on the basis of 1D and 2D NMR spectral data analysis, and the absolute stereochemistry of gymnothedelignans A and B was further confirmed by single crystal X-ray diffraction analysis. Graphical abstract image
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Palladium-catalyzed Suzuki cross-coupling of arylhydrazines via CNHNH2 bond activation in water ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Jin-Biao Liu , He-Ping Zhou , Yi-Yuan Peng A novel palladium-catalyzed Suzuki cross-coupling reaction of arylhydrazine with aryl boronic acid is described, which affords the corresponding biaryl compounds in good yields. This transformation proceeds through a CNHNH2 bond activation under green conditions. Graphical abstract image
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Synthesis of oxygenated 2-methylindolines ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Meng-Yang Chang , Yi-Chia Chen , Chieh-Kai Chan A palladium-mediated high-yielding synthesis of oxygenated 2-methylindolines 4 from 2-allylnitrobenzene 1 and hydrazine is developed. The one-pot route combines the reduction of 2-allylnitrobenzene 1 and the sequential intramolecular hydroamination. The protocol provides a novel alternative for the synthesis of substituted 2-methylindoline 4. Graphical abstract image
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A metal-free cross-dehydrogenative coupling of N-carbamoyl tetrahydroisoquinoline by sodium persulfate ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Wenfang Chen , Hongbo Zheng , Xinhui Pan , Zhiyu Xie , Xin Zan , Bin Sun , Lei Liu , Hongxiang Lou A metal-free cross-dehydrogenative coupling of N-carbamoyl tetrahydroisoquinoline with a variety of CH nucleophiles mediated by Na2S2O8 is developed. The reaction proceeds smoothly to give the coupled product in up to 83% yields. The nucleophile scope is broad, including simple ketones, aldehydes, and aryl rings. The carbamoyl protecting group can be readily removed under mild condition. The use of Na2S2O8 as the sole reagent for the CDC reaction is attractive based on economical and environmental factors. Graphical abstract image
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Efficient synthesis of trypsin inhibitor SFTI-1 via intramolecular ligation of peptide hydrazide ()
Publication date: 23 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 17 Author(s): Yi-Qun Chen , Chen-Chen Chen , Yao He , Mu Yu , Lin Xu , Chang-lin Tian , Qing-Xiang Guo , Jing Shi , Min Zhang , Yi-Ming Li Cyclic peptide trypsin inhibitor SFTI-1 was synthesized via intramolecular ligation of a linear peptide hydrazide with high yield. This cyclization strategy did not cause epimerization at the C-terminal Arg residue. CD spectrum and NMR spectroscopy analysis demonstrated that well-folded SFTI-1 could be obtained via standard oxidative folding process. Thus, we present a simple and cost-efficient strategy for the synthesis of SFTI-1. Graphical abstract image
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Facile synthesis of 3H, 3′H-spiro[benzofuran-2,1′-isoindole]-3, 3′-diones using monobromomalononitrile (MBM) as an efficient organo-brominating agent ()
Publication date: Available online 18 April 2014 Source:Tetrahedron Letters Author(s): Ashis Kundu , Sudipta Pathak , Kamalesh Debnath , Animesh Pramanik An efficient methodology for the synthesis of 3H,3′H-spiro[benzofuran-2,1′-isoindole]-3,3′-diones has been developed where monobromomalononitrile (MBM) has been employed as a non-hazardous brominating agent under ambient reaction condition. The intrinsic advantages of the methodology are the utilization of simple and easily available starting materials and non-toxic reagents, operational simplicity and good yields of the products with high atom-economy. Graphical abstract image Highlights
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Total synthesis of antifungal gamahonolide A ()
Publication date: Available online 18 April 2014 Source:Tetrahedron Letters Author(s): Gowravaram Sabitha , K. Purushotham Reddy , S. Purushotham Reddy , J.S. Yadav The first stereoselective total synthesis of gamahonolide A (1) has been accomplished using aminoxylation, Keck allylation and ring-closing metathesis (RCM) reactions as key steps. Graphical abstract image Highlights
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Editorial board ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16
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Graphical Contents List ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16
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Catalytic asymmetric synthesis of 3,3-disubstituted oxindoles: diazooxindole joins the field ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Zhong-Yan Cao , Yu-Hui Wang , Xing-Ping Zeng , Jian Zhou The catalytic asymmetric synthesis of 3,3-disubstituted oxindoles, a big family of privileged scaffolds in natural products and drugs, is of current interest. Recently, the catalytic asymmetric functionalization of diazooxindoles emerges as a potentially general and flexible strategy for this purpose, with several notable examples coming out in 2013. In this digest, synthetic applications of diazooxindoles have been summarized and discussed, which might be helpful for readers to understand the special properties of this type of donor/acceptor cyclic diazo reagent and to develop new catalytic asymmetric reactions. Graphical abstract image
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Stoichiometry-controlled cycloaddition of azomethine ylide with dipolarophiles: chemoselective and regioselective synthesis of bis- and tris-spirooxindole derivatives ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Srinu Lanka , Sathiah Thennarasu , Paramasivan T. Perumal A new series of bis- and tris-spirooxindole derivatives have been synthesized by controlling the molar equivalent of in situ generated azomethine ylides in [3+2]-cycloaddition reactions with dipolarophiles. The structural elucidation on the basis of IR, 1H NMR, 13C NMR, and mass spectral data of these compounds established the highly chemoselective and regioselective formation of spirooxindole derivatives. Single crystal X-ray analysis of compound 4g and 2D NMR analysis of compound 5a confirmed the structures of bis- and tris-spirooxindole derivatives. Graphical abstract image
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1,4-Zwitterionic intermediates formed by cleavage of a cyclobutane ring and their cycloaddition reactions ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Jun-ichi Matsuo Cycloaddition reaction is an efficient organic reaction because all of the substrate components are introduced into a product skeleton. Recently, more than six-membered rings have been synthesized by Lewis acid-promoted ring cleavage of a cyclobutane ring followed by addition to an unsaturated bond. Typical examples in the literature of these types of reactions using 1-donor–2-acceptor cyclobutanes and 3-donor cyclobutanones with Lewis acids are presented in this Letter. Graphical abstract image
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An elegant protocol for the synthesis of N-substituted pyrroles through C–N cross coupling/aromatization process using CuFe2O4 nanoparticles as catalyst under ligand-free conditions ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): G. Satish , K. Harsha Vardhan Reddy , K. Ramesh , B.S.P. Anil Kumar , Y.V.D. Nageswar A simple and efficient, ligand-free C–N cross-coupling of aryl halides/benzyl bromides with trans-4-hydroxy-l-proline has been developed to produce aromatized N-substituted pyrroles, using a catalytic amount of magnetically separable and recyclable CuFe2O4 nanoparticles, in the presence of Cs2CO3 in DMSO at 100°C. Graphical abstract image
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Hexanes/acetonitrile: a binary solvent system for the efficient monosilylation of symmetric primary and secondary diols ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Burkhardt I. Wilke , Mark H. Dornan , Jon Yeung , Christopher N. Boddy , Atahualpa Pinto Symmetric diols are useful compounds in the synthesis of natural products, their value often dependent on their successful monoprotection. A general and simple method for the monosilylation of symmetrical primary and secondary diols is reported. The method exploits the solubility differential of diols and their monosilylated counterparts in a binary hexanes/acetonitrile solvent system. Graphical abstract image Highlights
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Stereoselective tandem synthesis of oxazolo-fused pyrroloquinolines from o-alkynylaldehydes via Ag(I)-catalyzed regioselective 5-exo-dig ring closure ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Rajeev Ranjan Jha , Trapti Aggarwal , Akhilesh Kumar Verma A tandem approach for the regio- and stereoselective synthesis of oxazolo-fused pyrroloquinolines 3a–l via the reaction of o-alkynylaldehydes 1a–i with chiral amino alcohols 2a–c under mild reaction conditions is described. The possible participation of the pyridine ring in the regioselective formation of 5-exo-dig cyclized products was supported by the controlled experiments. The structures and stereochemistry of the products were confirmed by NOESY and X-ray crystallographic studies. Graphical abstract image
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Three-component synthesis of disubstituted 2H-pyrrol-2-ones: preparation of the violacein scaffold ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Emily C. McLaughlin , Matthew W. Norman , Thant Ko Ko , Ingrid Stolt An efficient, three-component, microwave-mediated cyclization to prepare the 3,5-disubstituted 2H-pyrrol-2-one core of the bis-indole alkaloid, violacein, is described. Preliminary results indicate an iterative, thermally driven, condensation of a γ-ketoester, ammonium acetate, and isatin in polyethylene glycol. This methodology is an effective and environmentally benign route to prepare a series of violacein analogs in good overall yields. Graphical abstract image Highlights
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TsOH-SiO2 as an efficient and eco-friendly catalyst for Knoevenagel condensation ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Zeba N. Siddiqui , Saima Tarannum Tosic acid on silica gel (TsOH-SiO2) was synthesized and characterized using microscopic and spectroscopic techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy. Thermal behaviour of the catalyst was investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TsOH-SiO2 showed excellent catalytic activity for the Knoevenagel condensation and was recyclable for six cycles. Graphical abstract image
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l-Proline catalyzed expeditious multicomponent protocol for the synthesis of fused N-substituted-2-pyridone derivatives in aqueous medium ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Rajib Sarkar , Chhanda Mukhopadhyay N-substituted-2-pyridone derivatives have many pharmaceutical properties. In our research, we have developed an efficient, green, and multicomponent protocol to synthesize such new fused N-substituted-2-pyridone derivatives. Optimum reaction condition was obtained by employing l-proline as an organocatalyst in aqueous SDS solution at 100°C. Various 1,3-diketones, including indane 1,3-dione with a range of aromatic and aliphatic amines were utilized to synthesize fused 2-pyridone derivatives. The isolation of a reaction intermediate confirmed our proposed mechanism. Water as a reaction medium improved the scope of the reaction methodology to a large extent. Graphical abstract image
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Design and synthesis of azobenzene template based sulfonamide for capture of HCAII: dependence of efficiency on E–Z geometry ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Partha Sarathi Addy , Baisakhee Saha , Arpita Panja , Amit Kumar Das , Amit Basak We report the synthesis of azobenzene template based sulfonamides 1 and 2 for capture of Human Carbonic Anhydrase II (HCAII). Out of these, 1 showed successful capturing of the protein, only when it is photo-isomerized to the Z form thus demonstrating the importance of spatial proximity of the reactive and selective functionalities. Graphical abstract image
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Unexpected rearrangements of rhodium carbenoids containing a pyrrolidin-1-yl group ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Julian Diehl , Reinhard Brückner Ketone- and ester-substituted diazo compounds, which contain a pyrrolidine moiety were treated with dirhodium tetraacetate generating the corresponding rhodium carbenoids. They were expected to insert into a CH bond of the pyrrolidine moiety but reacted differently. The ketone-substituted rhodium carbenoid underwent a Wolff rearrangement. The resulting ketene continued to react by lactamization and electrocyclic ring-opening and gave an acrylamide. The ester-substituted rhodium carbenoid underwent a [1.2]-shift of the (pyrrolidin-1-yl)methyl moiety, which resulted in a methacrylic ester. For each rearrangement a mechanism is suggested. Graphical abstract image
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A colorimetric and ratiometric fluorescent turn-on fluoride chemodosimeter and application in live cell imaging: high selectivity via specific SiO cleavage in semi aqueous media and prompt recovery of ESIPT along with the X-ray structures ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Shyamaprosad Goswami , Avijit Kumar Das , Abhishek Manna , Anup Kumar Maity , Hoong-Kun Fun , Ching Kheng Quah , Partha Saha A ratiometric fluorescent turn-on probe for fluoride ion, based on modulation of the excited-state intramolecular proton transfer (ESIPT) process by chemodosimetric desilylation pathway is reported. The probe SNBT (silyl protected hydroxynaphthalene benzothiazole moiety) shows a significant increase of ratiometric absorption band at 440nm and emission band at 477nm by the deprotection of fluoride mediated silyl bond cleavage in CH3CN–H2O (8/2, v/v, 25°C). The test strips based on SNBT and F− are fabricated, which can act as a convenient and efficient F− test kits. Furthermore, the biological application shows that it can be very useful as a selective fluoride probe in the fluorescence imaging of living cells. Graphical abstract image
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Vasicine as tridentate ligand for enantioselective addition of diethylzinc to aldehydes ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Mushtaq A. Aga , Brijesh Kumar , Abdul Rouf , Bhahwal A. Shah , Subhash C. Taneja The first report of natural l-vasicine as tridentate chiral ligand for the enantioselective addition of diethylzinc to a variety of aliphatic and aromatic aldehydes is described. The ligand generates R-isomer of the secondary alcohols upto 98%ee. The quinazoline structure possibly imparts rigidity to the ligand and hence, consistently high enantioselectivity. The importance of the quinazoline ring was also supported by the reaction with other related ligands, partially lacking the structural features, thus resulting in poor enantioselectivity. Graphical abstract image
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Polyhydroxylated macrolide isolated from the endophytic fungus Pestalotiopsis mangiferae ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Humberto E. Ortega , Young Yongchun Shen , Karen TenDyke , Nivia Ríos , Luis Cubilla-Ríos A new polyhydroxylated macrolide, named mangiferaelactone (1) was isolated from a solid culture of the endophytic fungus Pestalotiopsis manguiferae, together with ten known compounds [(6S,1′S)-LL-P880α; (6S,1′S,2′R)-LL-P880β; (1′S,2′R)-LL-880γ; (1′R)-dehydropestalotin; (−)-5-carboxylmellein; (−)-5-methylmellein; (−)-5-hydroxylmethylmellein; arabenoic acid; 5,6-dihydro-4-methoxy-2H-pyran-2-one; and the (−)-2-hexylidene-3-methylsuccinic acid]. P. manguiferae was isolated from Hyptis dilatata, a small shrub common in the central region of Panama. The structure of compound 1 was elucidated by a combination of spectroscopic methods (IR, MS, optical rotation, 1D and 2D NMR spectroscopy). The absolute configuration of 1 was established as 4R,7R,8R,9S by application of vibrational circular dichroism (VCD). Compound 1 showed a minimum inhibitory concentration (MIC) of 1.6863mg/mL against Listeria monocytogenes, and 0.5529mg/mL against Bacillus cereus. No activity was observed for compound 1 against Plasmodium falciparum or Trypanosoma cruzi; likewise, no cytotoxic activity was observed against A2058 and H522-T1 cells. Graphical abstract image
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N-arylation of carbamate-protected glycine derivatives via palladium catalysis ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Danielle Falcone , Ekundayo Osimboni , David J. Guerin A synthesis of N-aryl and N-heteroaryl amino acid derivatives using palladium catalysis is described. Several carbamate-protected glycine derivatives react with aryl and heteroaryl halides using a palladium/Xantphos catalyst system to access the desired synthons. Graphical abstract image
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Design and synthesis of 2-(1,3-dialkoxy-2-methylpropan-2-yl)-1,3-diarylpropanes as tethering units for folded H-stacking polymers ()
Publication date: 16 April 2014 Source:Tetrahedron Letters, Volume 55, Issue 16 Author(s): Ryota Moriai , Yu-suke Naito , Ryosuke Nomura , Shigeaki Funyu , Ken-ich Ishitsuka , Naoki Asano , Sentaro Okamoto 1,3-Diarylpropenes 9 having a 1,3-dialkoxy-2-methylpropan-2-yl group were designed as tethering monomers for folded H-stacking polymers, and were readily synthesized from 2-ethoxymethylidene malonate in four- or five-steps, including a facile sequential addition–elimination–addition reaction of benzyl zinc reagents. The preference for the closed (stacked) conformation in the resulting 2-substituted 1,3-diarylpropanes 9 was evaluated using MM2 calculations, 1H NMR analyses, and fluorescence measurements. Copolymerization of the resulting monomers 9 with compounds containing π-units provided polymers with blue-shifted UV-absorptions both in solution and as films, compared with that of a model compound containing a single π-unit. This optical property is unique to H-aggregated π-units. Graphical abstract image
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