Tetrahedron Letters

Editorial board ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12
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Graphical Contents List ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12
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Designing photoswitches for molecular solar thermal energy storage ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Anders Lennartson , Anna Roffey , Kasper Moth-Poulsen Solar energy conversion and solar energy storage are key challenges for a future society with limited access to fossil fuels. Certain compounds that undergo light-induced isomerisation to a metastable isomer can be used for storage of solar energy, so-called molecular solar thermal systems. Exposing the compound to sun light will generate a high energy photoisomer that can be stored. When energy is needed, the photoisomer can be catalytically converted back to the parent compound, releasing the excess energy as heat. This Letter gives examples of selected molecular solar thermal systems found in the literature. The focus of the Letter is on examples where molecular design has been used to improve the performance of the molecules, and as such it may serve as an inspiration for future design. The selected examples cover five widely studied systems, notably: anthracenes, stilbenes, azobenzenes, tetracarbonyl-fulvalene-diruthenium compounds and norbornadienes. Graphical abstract image
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Recent advances in C–Si bond activation via a direct transition metal insertion ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Linjie Li , Yuebao Zhang , Lu Gao , Zhenlei Song The C–Si bond activation via a direct transition metal insertion has recently gained growing attention in the organic chemical community. The process not only shows a new and unique entry to functionalize the C–Si bond, but also presents a powerful method to synthesize diverse organosilanes via formation of a new C–Si bond. This Digest is intended to highlight some elegant advances, which are categorized into strained silacycles, acyclic C(sp3)–Si, acyclic C(sp2)–Si, and C(sp)–Si bond activation. Graphical abstract image
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Formal carbo [3+3] annulation and its application in organic synthesis ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jing Feng , Bo Liu This review describes a set of approaches to generate functionalized carbocycles via [3+3] annulation and their usefulness for synthesizing frameworks of natural products. This approach relies heavily on the 1,3-dianion/1,3-dielectrophile strategy for annulations of ketones, enamines, 1,3-bis(silyl enol ethers), and other 1,3-dianionic synthons. Graphical abstract image
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Bio-inspired dimerisation of prenylated quinones directed towards the synthesis of the meroterpenoid natural products, the scabellones ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Susanna T.S. Chan , Michael A. Pullar , Iman M. Khalil , Emmanuelle Allouche , David Barker , Brent R. Copp Stirring 2-geranyl-6-methoxy-1,4-hydroquinone in pyridine/O2 or 2-geranyl-6-methoxy-1,4-benzoquinone in pyridine/N2 affords the dimeric meroterpenoid natural products, scabellones A–C in modest to low yields and also identifies 2-methoxy-6-(4-methylpent-3-en-1-yl)-1,4-naphthoquinone (scabellone E) as a new natural product. The corresponding reaction of the des-methoxy analogue, 2-geranyl-1,4-benzoquinone in degassed pyridine for three days afforded the natural product cordiachromene A (15% yield) and 6-(4-methylpent-3-en-1-yl)-1,4-naphthoquinone (12%), the latter being a likely biosynthetic precursor to the marine meroterpenoid alkaloids, conicaquinones A and B. Graphical abstract image
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Improved apparent enantioselectivity of a hydrolase by sequential hydrolysis and racemization ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jiali Gu , Lidan Ye , Fei Guo , Xiaomei Lv , Wenqiang Lu , Hongwei Yu Further improvement of the enantioselectivity of hydrolases with moderate enantioselectivity is of important significance to fulfill the requirement in industrial application. Herein, a strategy based on sequential hydrolysis and racemization was adopted, using esterase BioH from Escherichia coli as an example. After coupling with a mandelate racemase, the E value of esterase BioH toward methyl (S)-o-chloromandelate was enhanced from 73 to 162, demonstrating the effectiveness of this strategy. Graphical abstract image
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An efficient one-pot synthesis of 2-bromo-6-aryl[5H]pyrrolo[2,3-b]pyrazines ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Iain Simpson , Steve A. St-Gallay , Stephen Stokes , David T.E. Whittaker , Rafal Wiewiora We report a two step one-pot method for the synthesis of 2-bromo-6-aryl[5H]pyrrolo[2,3-b]pyrazines. The process makes use of a cleaner copper-free Sonogashira coupling and an improved base-mediated 5-exo-dig cyclisation to afford the products in good yields. This method expands the scope to structures that are poorly represented in the literature and incorporates a halide for further synthetic elaboration. Graphical abstract image
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A novel, simple and effective synthesis of the hydroxybenzyl derivative of resorcinarene and the modification possibilities thereof ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Waldemar Iwanek , Karolina Stefańska A simple and efficient synthesis of the hydroxybenzyl derivative of resorcinarene has been developed, and possibilities for its modification have been shown on selected examples. Based on mass spectrometry, a mechanism for the course of the reaction of the hydroxybenzyl derivative of resorcinarene with aliphatic alcohols via formation of intermediate o-quinomethine derivatives of resorcinarene has been proposed. Graphical abstract image
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BF3·Et2O catalyzed allylation of oxindoles with allyl trichloroacetimidate ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jiao Ma , Ling Zhou , Jie Chen An efficient Lewis acid catalyzed allylation of 3-substituted oxindoles has been developed for the first time using allyl trichloroacetimidate as an electrophile under mild reaction conditions. Graphical abstract image
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Intramolecular aminochalcogenation and diamination of alkenes employing N-iodosuccinimide ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jun Zhang , Xuejun Zhang , Weijie Wu , Gengtao Zhang , Sheng Xu , Min Shi A NIS-mediated intramolecular diamination and aminosulfuration of alkenes with N-alkyl or N-aryl thioureas is reported. A chiral cyclic thiourea was also synthesized by the methodology. The protocol is also proven to be efficient in the intramolecular diamination and/or aminooxygenation of alkenes with N-alkyl or N-aryl ureas and ones with N-carbamate sulfamides. The resulting bicyclic thiourea could be further transformed into bicyclic guanidine. Graphical abstract image
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A one-pot, catalyst-free synthesis of novel 2-thioxo-tetrahydropyrimidine derivatives via the three-component reaction of alkyl chloroglyoxalates, alkyl isocyanides, and thioureas ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Loghman Moradi , Chonor Bahrami , Anvar Mirzaei , Mohammad Rezgar Zarehbin , Issa Yavari α-Ketoimidoyl chlorides, obtained from the α-addition of acyl chlorides to alkyl isocyanides are treated with thiourea derivatives to afford novel 2-thioxo-tetrahydropyrimidine derivatives in good to excellent yields. Graphical abstract image
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Synthesis of dibenzo[b,d]furans through one-pot cascade reactions of 1-arylpenta-3,4-dien-2-ones with activated ketones ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Yan He , Shenghai Guo , Xinying Zhang , Chenhao Guo , Xuesen Fan One-pot cascade reaction of 1-arylpenta-3,4-dien-2-ones with activated ketones including base-promoted Michael addition/intramolecular aldol condensation/copper-catalyzed C–H activation and annulation offers a simple and convenient approach toward dibenzo[b,d]furans. This reaction obviates highly functionalized starting materials and step by step operations and affords products with good efficiency and high sustainability. Graphical abstract image
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Copper-catalyzed synthesis of 1,2-diketones via oxidation of alkynes ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Ning Xu , Da-Wei Gu , Yan-Sheng Dong , Feng-Ping Yi , Liangzhen Cai , Xin-Yan Wu , Xun-Xiang Guo The direct oxidation of internal alkynes proceeds efficiently in the presence of CuI as a catalyst to afford the corresponding 1,2-diketones in good yields. This strategy offers a simple and efficient route for the synthesis of 1,2-diketones from an inexpensive copper catalyst and easily available internal alkynes. The advantage of present protocol is further demonstrated by the synthesis of quinoxaline derivatives from alkynes and 1,2-diaminobenzene via one-pot procedure. Graphical abstract image
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Electrochemical hydrodefluorination of fluoroaromatic compounds ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Wen-Bin Wu , Mei-Li Li , Jing-Mei Huang The BH4 −- promoted electrochemical hydrodefluorination of fluoroaromatic compounds was reported. Using platinum as electrodes in an undivided cell, the electrolysis was carried out at constant current at room temperature under air without the need of pretreatment of the solvent. This reaction could proceed smoothly on both nonactivated monofluoroarenes and perfluoroarenes with high yields and good selectivities. Graphical abstract image
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Organic hypervalent iodine(III) catalyzed ipso-hydroxylation of aryl- and alkylboronic acids/esters ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Nachiketa Chatterjee , Avijit Goswami An organo-hypervalent iodine(III) catalyzed highly efficient methodology for ipso-hydroxylation of diversely functionalized aryl- and alkylboronic acids/esters has been developed using NaIO4 as a co-oxidant. This protocol is also applicable to N-heterocyclic boronic acids and esters. Further mechanistic studies revealed that the organoboronic acid (an electron demanding moiety) is acting as a nucleophile in the presence of hypervalent iodine for hydroxylation reactions. In summary, this is the first Letter of a generalized route for organic hypervalent iodine(III) catalyzed hydroxylation of organoboronic compounds. Graphical abstract image
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Facile synthesis of new 10-substituted-5H-naphtho[1,2-e][1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-5-ones ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jabbar Khalafy , Mahsa Mohammadlou , Miri Mahmoody , Fatemeh Salami , Ahmad Poursattar Marjani The reaction of 2-bromo-1,4-naphthoquinone with 4-amino-5-aryl-4H-1,2,4-triazole-3-thiols in ethanol at 50°C gave the corresponding 2-[(4-amino-5-aryl-4H-1,2,4-triazol-3-yl)thio]naphthalene-1,4-diones. Their treatment with EtOH/HCl under reflux conditions produced 10-substituted-5H-naphtho[1,2-e][1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-5-ones through intramolecular cyclization. Graphical abstract image
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AlCl3-catalyzed insertion of isocyanides into nitrogen–sulfur bonds of sulfenamides ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Daisuke Shiro , Shin-ichi Fujiwara , Susumu Tsuda , Takanori Iwasaki , Hitoshi Kuniyasu , Nobuaki Kambe Lewis acid-catalyzed insertion of isocyanides 2 into nitrogen–sulfur bonds of sulfenamides 1 was developed. This method provided a convenient method for the synthesis of isothioureas 3. Among Lewis acids examined, AlCl3 brought about the best result. Acetic acid assisted one-pot preparation of unsymmetrical ureas was also described. Graphical abstract image
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Fullerene recognition by 5-nitro-11,17,23,29-tetramethylcalix[5]arene ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Karolína Flídrová , Alan Liška , Jiří Ludvík , Václav Eigner , Pavel Lhoták The condensation of different building blocks allows the synthesis of an electrochemically active 5-nitro-11,17,23,29-tetramethylcalix[5]arene that was designed to study fullerene complexation using cyclic voltammetry. Although this method was ultimately unsuccessful, the formation of complexes between the calix[5]arene derivative and C60 or C70 fullerenes in solution was proved by mass spectrometry. Moreover, the solid state structure of the complex with fullerene C60 was confirmed by X-ray crystallography. Graphical abstract image
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A tactical 1,3-dipolar cycloaddition approach for the synthesis of carbohydrate derived polycyclic spiro heterocycles ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): J. Naga Siva Rao , R. Raghunathan A facile one-pot synthesis of carbohydrate derived spiro heterocycles via [3+2] cycloaddition reaction of azomethine ylides is described. A unique dipolarophile synthesized from d-glucose reacted with azomethine ylide generated in situ from secondary α-amino acids (sarcosine, proline, or pipecolinic acid) and 1,2-diketone (isatin/acenaphthoquinone)/indenoquinoxalinone to give their corresponding cycloadducts in good yield. The regio- and stereochemical outcome of the cycloaddition reaction is ascertained by X-ray crystallographic analysis. Graphical abstract image
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A novel transformation of β-1,2,3-thiadiazol-5-yl enamines into thieno[2,3-d]pyridazines ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Yuri Rozin , Sergey Zhidovinov , Tetyana Beryozkina , Yuri Shafran , Gert Lubec , Oleg Eltsov , Pavel Slepukhin , Uwe Knippschild , Joachim Bischof , Wim Dehaen , Vasiliy Bakulev Reactions of β-1,2,3-thiadiazol-5-yl enamines with acetyl chloride in 1,4-dioxane lead to the formation of either dienamines or novel thieno[2,3-d]pyridazines depending on the time and reaction temperature. Conditions were found for the selective synthesis of thieno[2,3-d]pyridazines. A plausible mechanism involves formation of C–S and C–C bonds and a novel ring rearrangement of 5-vinyl-1,2,3-thiadiazoles into pyridazine-4-thiolates. A series of new diamides of 2-(4-carboxy-1,2,3-thiadiazol-5-yl)thieno[2,3-d]pyridazine-7-carboxylic acid is prepared by reaction of the methyl ester with primary and secondary amines. Graphical abstract image
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Synthesis and electronic properties of ferrocene-containing organic dyads ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Motonori Watanabe , Yuan Jay Chang , Po-Ting Chou , Aleksandar Staykov , Masahiko Shibahara , Katsuya Sako , Tatsumi Ishihara , Tahsin J. Chow Novel ferrocene–oligothiophenylene–cyanoacrylic acid in the form of donor–spacer–acceptor dyads was synthesized. The compound with a single unit of thiophenylene showed the lowest energy transition in neutral state. For radical cations, the lowest energy transition appears red-shifted along with the increased number of thiophenylene units. These results suggested that the electronic structure of radical cations is significantly different from that of neutral molecules. Graphical abstract image
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Reactions of 5-substituted 1,3,4-thiadiazole-2-thiones with chloroacetylenephosphonates ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Dmitrij M. Egorov , Yulija L. Piterskaya , Albina V. Dogadina , Nataly I. Svintsitskaya Reactions of 1-chloroacetylene-2-phosphonates with thiadiazole-2-thiones in anhydrous acetonitrile occur regio- and chemoselectively to form novel fused phosphorus-containing heterocycles, 2-substituted 5-(dialkoxyphosphoryl)thiazolo[2,3-b][1,3,4]thiadiazol-4-ylium chlorides. The formation of these fused cyclic compounds is associated only with the thione form of the starting thiadiazoles. Reactions of the salts of thiadiazole-2-thiols with 1-chloroacetylene-2-phosphonates result in the formation of compounds of linear structure. Graphical abstract image
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SnCl4–Zn: a novel reductive system for deoxygenative coupling of aliphatic, aromatic, chalcone epoxide, and indanone carbonyl compounds to olefins ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Gulab Khushalrao Pathe , Naseem Ahmed SnCl4–Zn complex provided a novel reductive system in the deoxygenative cross-coupling of aliphatic, aromatic, chalcone epoxide and indanone carbonyl compounds to olefins in high yield (55–86%) at reflux temperature in THF. The advantage of this reagent is inexpensive, short reaction time, and high yield compared to the reagents used in the McMurry cross-coupling reaction. Graphical abstract image
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Syntheses of phosphorylcholine-substituted silsesquioxanes via thiol-ene ‘click’ reaction ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Lei Liu , Su Jung Lee , Myong Euy Lee , Philjae Kang , Moon-Gun Choi Phosphorylcholine-substituted silsesquioxanes were synthesized via the UV-initiated thiol-ene ‘click’ reaction of octakis(3-mercaptopropyl)octasilsesquioxane (POSS-SH) with 2-methacryloyloxyethylphosphorylcholine or allylphosphorylcholine in mixed (DMF/MeOH) solvents, respectively. In addition, the crystal structures of POSS-SH and MPC were first determined. Graphical abstract image
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Use of a fluorescent aminodeoxylactitol to measure the stability of anti-HIV catanionic dendrimers by spectrofluorimetry ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Alexandra Perez-Anes , Serge Mazères , Anne-Marie Caminade , Muriel Blanzat , Cédric-Olivier Turrin The dissociation constants (K D) of anti-HIV catanionic dendrimers have been evaluated spectroscopically by means of fluorescent analogs of the aminolactitol which is involved in the stoichiometric ion pairing systems comprising PolyPhosphorHydrazone (PPH) dendrimers with various types of organic acid surface functions. This study elucidates the origin of the low therapeutic index of these anti-HIV catanionic dendrimers which were previously reported to exhibit in vitro anti-HIV activity in the sub-micromolar range. Graphical abstract image
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α-Glucosidase inhibitory monoacylated polyhydroxytriterpenoids from the fruits of Barringtonia racemosa ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Mangala Gowri Ponnapalli , Sushma Sukki , S.CH.V. Appa Rao Annam , Madhu Ankireddy , Harini Tirunagari , V. Raju Tuniki , V.V. Pardhasaradhi Bobbili Chemical investigation of a lipophilic CHCl3 extract of the dried fruits of Barringtonia racemosa resulted in the isolation of two unusual monoacylated polyhydroxy oleanane triterpenoid congeners named racemosols C–D (1–2) along with three known compounds. Their structures were determined by comprehensive spectroscopic analysis coupled with chemical modifications as 21β-acetoxy-3β, 16α,22α,28-tetrahydroxyolean-12-ene (1) and 22α-(2-methylbutyryl)-3β, 15α,16α,21β,28-pentahydroxyolean-12-ene (2). Compounds (1–3, 1a, and 2a) were subjected to α-glucosidase inhibitory assay and 1 showed the most potent α-glucosidase inhibition with an IC50 value of 5.6μM. Graphical abstract image
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Copper-catalyzed base-accelerated direct oxidation of C–H bond to synthesize benzils, isatins, and quinoxalines with molecular oxygen as terminal oxidant ()
Publication date: 18 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 12 Author(s): Jing-Wen Yu , Shuai Mao , Yong-Qiang Wang We describe herein an efficient and general copper (II)-catalyzed base-accelerated oxidation of the C–H bond to synthesize benzils and isatins. With similar oxidation system an efficient one-pot procedure for the synthesis of quinoxaline derivatives was realized. The two protocols feature using molecular oxygen as terminal oxidant, low catalyst loading, wide substrate scope, and high functional-group tolerance. Graphical abstract image
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Editorial board ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11
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Graphical Contents List ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11
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Palladium-catalyzed decarboxylative cross-coupling of 3-pyridyl and 4-pyridyl carboxylates with aryl bromides ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Lohitha Rao Chennamaneni , Anthony D. William , Charles W. Johannes Decarboxylative cross-coupling of 3-pyridyl and 4-pyridyl carboxylates with aryl bromides is reported. Using a bimetallic system of Cu2O and Pd(PPh3)4, the scope of the reaction is demonstrated by the synthesis of 27 pyridine-containing biaryls in moderate to good yields. Graphical abstract image
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On the origins of regioselectivity in the orthoester Claisen rearrangement of bisallylic alcohols ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Brian M. Lawrence , DeMarcus K. Crews When used as a strategy for selective carbon–carbon bond formation, the Johnson–Claisen rearrangement has proven extremely useful in the synthesis of complex natural products. Our attempts to prepare terminal diene esters as part of a modular strategy for the synthesis of Actinofuranone B has led us to investigate this reaction process further, especially in relation to the desymmetrization of bisallylic alcohols. In the present work, we revisit mechanistic studies that suggest that this type of rearrangement is best described as a [3,3] sigmatropic shift and subsequently present the results of our computational study of the Johnson–Claisen [3,3] sigmatropic rearrangement. Herein, evidence is presented to support our hypothesis that electronic considerations in the transition states of this reaction type oft dominate the product selectivities observed for this class of [3,3] sigmatropic rearrangements. Graphical abstract image
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Supported nano gold catalyzed three-component coupling reactions of amines, dichloromethane and terminal alkynes (AHA) ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Amina Berrichi , Redouane Bachir , Mohamed Benabdallah , Noureddine Choukchou-Braham A simple and efficient method for the synthesis of pharmaceutically relevant propargylamines through one-pot three-component coupling reactions of amines, CH2Cl2, and terminal alkynes (AHA) using nano Au/CeO2 as a heterogeneous catalyst is reported. The catalyst is characterized by DRX, DR-UV visible spectroscopy, and TEM. Gold particles are regularly distributed on ceria and range in size from 2 to 4nm. Graphical abstract image
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Nickel catalyzed [3+2] cycloaddition reaction of bis(methylenecyclopropane) with cyclic and acyclic dienophiles ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Bilash Kuila , Dinesh Mahajan , Prabhpreet Singh , Gaurav Bhargava Nickel catalyzed [3+2] cycloaddition reactions of bis(methylenecyclopropane) with cyclic and acyclic dienophiles have been explored. The reactions resulted in the formation of functionalized cyclopentanes in good yields. The reactions were also explored under microwave irradiation for the first time to yield [3+2] cycloadducts in short reaction time and high yields. Graphical abstract image
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Dual-immobilized copper catalyst: carbon nitride-supported copper nanoparticles catalyzed oxidation of propargylic alcohols ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Wei Lv , Jing Tian , Nan Deng , Yan Wang , Xiaoshu Zhu , Xiaoquan Yao Copper nanoparticles were supported and modified by carbon nitride, which was utilized as support and might work as a kind of immobilized N-donor ligand. The modified nanoparticle catalyst was evaluated with the oxidation of propargylic alcohols and showed highly catalytic efficiency as well as significant ligand or support effect in the reaction. The dual-immobilized nanoparticle catalyst could be recycled for 3 times at least without an obvious decrease in catalytic activities. Graphical abstract image
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Nucleophile-dependent diastereoselectivity in the ring expansion of pyrimidines to give 1,3-diazepines ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Anastasia A. Fesenko , Ludmila A. Trafimova , Dmitry V. Albov , Anatoly D. Shutalev A five-step synthesis of 4-(1-mesyloxyethyl)-6-methyl-5-tosyl-1,2,3,4-tetrahydropyrimidin-2-one via amidoalkylation has been developed. Reactions of this compound with C-, O-, S-, and N-nucleophiles led to the highly diastereoselective formation of polysubstituted 2,3,4,5-tetrahydro-1H-1,3-diazepin-2-ones as a result of ring expansion. The diastereoselectivity of the reactions depended on the nucleophile used and changed from cis to trans. The results obtained were explained by the formation of a bicyclic cyclopropane intermediate followed by cleavage of the zero bridge and stereoselective addition of the nucleophile to the resulting dihydro-1H-1,3-diazepin-2-one under kinetic control. The prepared cis-4-alkoxy-5-methyldiazepines reacted with alcohols under acidic conditions to give thermodynamically more stable trans-isomers. When harsh acidic conditions were used, ring contraction of 4-alkoxydiazepines to give 1-carbamoyl-1H-pyrroles was observed. Graphical abstract image
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A new fluorescent sensor for Cd2+ and its application in living cells imaging ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Xiao-yan Liu , Da-ying Liu , Jing Qi , Zhi-gang Cui , He-xi Chang , Hua-rui He , Guang-ming Yang A novel, fluorescent sensor based on 2,7-dichlorofluorescein with aromatized diethylene triamine as ionophore was developed. Under physiological pH conditions, the sensor exhibited about 70-fold enhancement in fluorescence emission upon binding with Cd2+. It demonstrates that the sensor can be used to detect Cd2+ in aqueous solution and it was successfully applied to image Cd2+ in living cells. Graphical abstract image
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A pair of novel 2,3-seco cafestol-type diterpenoid epimers from the twigs of Tricalysia fruticosa ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Chuan-Pu Shen , Jian-Guang Luo , Ming-Hua Yang , Ling-Yi Kong A pair of 2,3-seco cafestol-type diterpenoid epimers, frutilactones A (1) and B (2) were isolated from twigs of Tricalysia fruticosa. Their structures were elucidated by comprehensively employing spectroscopic methods (MS and 1D/2D NMR) and ECD. Their inhibitory effects on nitric oxide production in lipopolysaccharide-activated macrophages were evaluated, and a possible biogenetic pathway was also proposed. Graphical abstract image
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A simple one-pot preparation of 3,3a-dihydro-5H-pyrano[3,3a-c]isoxazol-5-ylideneethanal from 4-vinyloxyphenyl azide: an example of aromatic azide photooxidation for the synthesis of nitrogen-containing heterocyclic compounds ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Ekaterina Chainikova , Aigul Teregulova , Alexander Lobov , Alexey Erastov , Rustam Safiullin Photolysis of 4-vinyloxyphenyl azide in the presence of oxygen in acetonitrile leads to the formation of a fused heterocyclic compound due to the ability of the intermediates of this reaction to undergo a unique domino reaction sequence. The rate constants and activation parameters of some elementary stages of the process are measured by flash photolysis. Graphical abstract image
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α-(N-Sulfonyl)amino amides from a carbamoylsilane and N-sulfonylimine ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Wenting Tong , Hui Liu , Jianxin Chen Under using anhydrous benzene as a solvent, and no catalyst, N,N-dimethylcarbamoyl (trimethyl)silane reacts with N-sulfonylimines at 60°C to afford α-(N-sulfonyl)amino amides derivatives in good yields (71–89%). The electronic property of the substituted group on the aryl ring affects the reaction. Graphical abstract image
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Condensation of salicylaldehydes with ethyl 4,4,4-trichloro-3-oxobutanoate: a facile approach for the synthesis of substituted 2H-chromene-3-carboxylates ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Mudulkar Sairam , Gannerla Saidachary , Bhimapaka China Raju A highly efficient and simple protocol has been developed for the preparation of ethyl 2-oxo-2H-chromene-3-carboxylates 3a–v by the condensation of salicylaldehydes 1a–v with ethyl 4,4,4-trichloro-3-oxobutanoate 2 for the first time. The reaction is proceeding via Knoevenagel pathway followed by a selective addition of the phenolic hydroxyl group to the carbonyl group adjacent to the CCl3 group rather than ester carbonyl due to a strong electron withdrawing effect and produced coumarin derivative 3a with the elimination of CHCl3. Graphical abstract image
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Studies toward the total synthesis of (+)-etharvendiol ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Ramesh Kunde , Kallaganti V.S. Ramakrishna , Palakodety Radha Krishna Studies toward the total synthesis of styryllactone natural product (+)-etharvendiol is described using d-glucono-δ-lactone, stereoselective phenyl Grignard addition, Still–Gennari olefination, and acid catalyzed one pot deprotection and lactonization as the key steps. Graphical abstract image
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Sarcophytrols A–C, new capnosane diterpenoids from the South China Sea soft coral Sarcophyton trocheliophorum ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Wen-Ting Chen , Li-Gong Yao , Xu-Wen Li , Yue-Wei Guo Three new capnosane type diterpenoids, sarcophytrols A–C (1–3), were isolated from the South China Sea soft coral Sarcophyton trocheliophorum. Among them, 1 and 2 share a dodecahydrocyclopenta[6,7]cycloundeca[1,2-b]oxirene ring system with an unusual 1Z-configuration, whereas 1 and 3 encompass a peculiar isopropyl alcohol moiety. Their structures were elucidated by extensive spectroscopic analysis and the absolute configuration of 1 was determined by an X-ray diffraction analysis with Cu Kα radiation on a single crystal. Graphical abstract image
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Transition-metal-free direct amination of simple arenes with sulfonyl azides ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Lianggui Wang , Arun Jyoti Borah , Guobing Yan A metal-free green protocol has been developed for amination of simple arenes using arylsulfonyl azides via a nitrene transfer process under solvent free conditions at 130°C releasing N2 gas as the sole by-product. Graphical abstract image
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Total synthesis of (3R,16E,20E,23R)-(−)-eushearilide and structural determination of naturally occurring eushearilide ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Takayuki Tonoi , Ryo Kawahara , Yutaka Yoshinaga , Takehiko Inohana , Keiko Fujimori , Isamu Shiina An asymmetric total synthesis of the proposed structure of (16Z,20E)-eushearilide, a novel 24-membered macrolide, was achieved via an enantioselective aldol reaction and 2-methyl-6-nitrobenzoic anhydride-mediated macrolactonization. The obtained synthetic compounds were not identical to the natural product. The newly proposed most likely structure of eushearilide, (±)-(16E,20E)-eushearilide, was determined on the basis of detailed NMR analysis, and (3R,16E,20E,23R)-(−)-eushearilide was successfully synthesized. A comparison of the optical rotation of (3R,16E,20E,23R)-(−)-eushearilide with that of the natural product confirmed that the true structure of naturally occurring eushearilide is the (3S,16E,20E,23S)-(+)-form. Graphical abstract image
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Enantioselective syntheses of diarylheptanoids (2R,4S,6R)-2-(4-hydroxyphenethyl)-6-(4-hydroxyphenyl) tetrahydro-2H-pyran-4-ol and (3R,5R)-1,7-bis(4-hydroxyphenyl)heptane-3,5-diol ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Jhillu Singh Yadav , Eppa Gyanchander , Sheshurao Bujaranipalli , Saibal Das The first total syntheses of diarylheptanoid natural products (2R,4S,6R)-2-(4-hydroxyphenethyl)-6-(4-hydroxyphenyl) tetrahydro-2H-pyran-4-ol (4) and (3R,5R)-1,7-bis (4-hydroxyphenyl)heptane-3,5-diol (12) were accomplished using substrate selective hydrogenation, ring cleavage of tetrahydropyran ring, and Keck–Maruoka allylation as the key synthetic steps. Graphical abstract image
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A medium fluorous Grubbs–Hoveyda 2nd generation catalyst for phase transfer catalysis of ring closing metathesis reactions ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Yuki Kobayashi , Sae Inukai , Natsuki Kondo , Tomoko Watanabe , Yuya Sugiyama , Hiromi Hamamoto , Takayuki Shioiri , Masato Matsugi A fluorous Grubbs–Hoveyda metathesis catalyst supported on Teflon® powder, that readily moves between the solid phase (Teflon®) and the liquid phase (DMF) was prepared. By modulating the hydrophobicity of the reaction medium at the end of the reaction, the supported catalyst could be recovered by simple filtration even though the catalyst existed in a homogeneous state during the reaction. In RCM reactions, the catalyst could be reused up to three times with only a slight loss in reactivity with each subsequent cycle. Graphical abstract image
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Pyrazoloquinazolinones and pyrazolopyridopyrimidinones by a sequential N-acylation–SNAr reaction ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Krishna Kumar Gnanasekaran , N. Prasad Muddala , Richard A. Bunce An efficient synthesis of pyrazolo[1,5-a]quinazolin-5(4H)-ones and pyrazolo[1,5-a]pyrido[3,2-e]pyrimidin-5(4H)-ones is reported from the reaction of 2-haloaroyl chlorides with 5-amino-1H-pyrazoles. The reaction takes advantage of the 1,3-disposition of electrophilic centers in the acid chloride and the similar arrangement of nucleophilic sites in the pyrazole to form the central six-membered ring. Initial acylation of the C5 amino group of the pyrazole is performed in DMF at −10°C, and subsequent heating to 140°C, in the same reaction vessel, completes the synthesis via an SNAr ring closure between N1 of the pyrazole and the 2-haloarylamide. The reaction gives yields of 66–93% for the two-step sequence. Graphical abstract image
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Peptidyl N-alkylcysteine as a peptide thioester surrogate in the native chemical ligation ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Yuya Asahina , Kei Nabeshima , Hironobu Hojo Peptides having the C-terminal N-alkylcysteine (NAC) with a free carboxy group, which can be easily prepared by the conventional 9-fluorenylmethoxycarbonyl (Fmoc) solid-phase peptide synthesis (SPPS), was directly used for the native chemical ligation (NCL) based on the in situ thioesterification method. The reaction efficiently proceeded under a mild acidic condition (pH ∼5) to give the ligated product. This method was successfully used for the synthesis of the human brain natriuretic peptide, (BNP)-32, showing the usefulness of the peptidyl NAC as a thioester surrogate for the NCL reaction. Graphical abstract image
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Intermolecular coupling of 2-iodoanilides with benzoxazoles: synthesis of N-(2-Benzoxazol-2-ylphenyl)benzamides via C–H activation ()
Publication date: 11 March 2015 Source:Tetrahedron Letters, Volume 56, Issue 11 Author(s): Swarnendu Sasmal , Indira Sen , Roger G. Hall , Sitaram Pal Using CuI/xantphos/Pd(OAc)2 catalytic system, the intermolecular C–C cross coupling between benzoxazoles and ortho-haloanilides has been developed in moderate to good yields. The procedure tolerates a series of functional groups on benzoxazole, such as ester, chloro, methyl, and methoxy groups. This divergent approach provides access to various N-(2-Benzoxazol-2-ylphenyl)amides. Graphical abstract image
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