Tetrahedron Letters

Editorial board ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18
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Microwave-assisted transamidation of ureas ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Tammy C. Wang, Jennifer X. Qiao An effective microwave-assisted urea formation from cyclopentyl- or isopropyl-substituted ureas is described. This novel transamidation methodology provided ureas IIa–IIq in good yields via microwave irradiation of the cyclopentyl- or isopropyl-substituted ureas with excess (5–10equiv) of amines at 150°C in THF/DMSO. Graphical abstract image
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Insight into the role of halogen bond in the activity of d-mandelate dehydrogenase toward halogenated substrates ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Fei Guo, Lidan Ye, Aipeng Li, Xiaohong Yang, Chengcheng Yang, Hongwei Yu Chlorine substitution in mandelate turned its derivatives into less active substrates for d-mandelate dehydrogenase (DMdh). To improve the catalysis of chloro-mandelate, a halogen bond was introduced into the protein–substrate complex by site mutation. The catalytic activity of the resulting mutant A89H toward o-chloromandelate was improved by 5 times. The effect of halogen bond was also observed in the dehydrogenation of m-chloromandelate and p-chloromandelate. Based on these results, a new insight was proposed for the role of halogen bond in enzyme activity, and the introduction of halogen bond was shown as an efficient strategy to optimize the catalytic activity toward halogenated substrates. Graphical abstract image
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A catalyst and additive-free three-component reaction of highly electrophilic azides with cyclic ketones and cycloaliphatic amines. Synthesis of novel N-heteroaryl amidines ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Ilya Efimov, Nikolai Beliaev, Tetyana Beryozkina, Pavel Slepukhin, Vasiliy Bakulev Highly electrophilic 5-azido-1-methyl-4-nitro-1H-imidazole and sulfonyl azides were demonstrated to react with alicyclic amines and cyclic ketones in the absence of any catalyst or additive to afford novel N-(4-nitroimidazol-5-yl)- or N-sulfonylamidines respectively. Based on single crystal X-ray analysis, a revision of the previously reported data of Gao and co-workers on the direction of the reaction of sulfonyl azides with endocyclic enamines was made. The reaction of 2,6-diazidopyridine with an enamine, 4-(cyclohex-1-en-1-yl)morpholine, proceeded with cyclization of the azide moiety onto the pyridine CN bond to form an amidine bearing the tetrazolo[1,5-a]pyridine fragment. Graphical abstract image
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Synthetic study on the T3P®-promoted one-pot preparation of 1-substituted-3,4-dihydro-β-carbolines by the reaction of tryptamine with carboxylic acids ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Péter Ábrányi-Balogh, Tamás Földesi, Alajos Grün, Balázs Volk, György Keglevich, Mátyás Milen A novel and efficient one-pot method has been developed for the synthesis of 1-substituted-3,4-dihydro-β-carbolines from tryptamine and a wide variety of carboxylic acids. The reaction was successfully applied to the synthesis of an important alkaloid harmalan as well as dihydro-eudistomin-U. This represents the first case in which 1-propanephosphonic acid cyclic anhydride (T3P®) has been used in the Bischler–Napieralski reaction. Unexpectedly it was observed that less than two equivalents of the T3P® reagent were sufficient for the two consecutive reactions. Graphical abstract image
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Synthesis of 1,8-naphthyridines from 2-aminonicotinaldehydes and terminal alkynes ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Binbin Li, Steven Nguyen, Jianjun Huang, Gaigai Wang, Huiping Wei, Olga P. Pereshivko, Vsevolod A. Peshkov A copper(II) triflate-catalyzed diethylamine-assisted protocol for the reaction of 2-aminonicotinaldehydes and terminal alkynes leading to 1,8-naphthyridines is described. The overall process presumably involves a copper(II) triflate-catalyzed hydroamination of the triple bond followed by the Friedländer-type condensation of the resulting enamine with 2-aminonicotinaldehyde. Graphical abstract image
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Synthesis and photochromism of a novel amphiphilic diarylethene bearing two cholic acid groups ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Fang Duan, Gang Liu, Congbin Fan, Shouzhi Pu A novel amphiphilic diarylethene with two cholic acid groups, 1,2-bis[2-methyl-5-[3-(1,2,3-triazole)methyl-5-cholic acid-3-thienyl]perfluorocyclopentene, has been successfully synthesized by click reaction for the first time and its photochromic, fluorescence, and electrochemistry properties were systematically investigated. This new compound showed good hydrophilia in methanol/water binary solution (v/v, 1:19). It exhibited photochromism with the notable color change from colorless to red and good fatigue-resistance by photoirradiation. Further study indicated that it also has excellent fluorescence switching property in methanol/water binary solution. Graphical abstract image
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Analysis of reaction products of astaxanthin and its acetate with reactive oxygen species using LC/PDA ESI-MS and ESR spectrometry ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Azusa Nishino, Takashi Maoka, Hiroyuki Yasui Reaction products of astaxanthin and its acetate with hydroxy radical, superoxide anion radical, and singlet oxygen were analyzed by LC/PDA ESI-MS and ESR spectrometry. Astaxanthin epoxides were found to be major reaction products of astaxanthin with superoxide anion radical and hydroxyl radical. On the other hand, astaxanthin endoperoxides were identified as major reaction products of astaxanthin with singlet oxygen. The same results were obtained in the case of astaxanthin acetate. The ESR study revealed that astaxanthin and its acetate take up superoxide anion radical by the formation of their epoxide through peroxide and oxide radicals. Graphical abstract image
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Pre-organized molecular tweezer stabilized by intramolecular hydrogen bonds: solvent-responsive host–guest complexation ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Xiaoqin Lv, Yifei Han, Zhishuai Yang, Zijian Li, Zhao Gao, Feng Wang A novel molecular tweezer consisting of 2,2′-iminodibenzoyl backbone and alkynylplatinum(II) terpyridine pincers is designed and synthesized. It shows moderate binding strengths towards two neutral organometallic guests, accompanying with interesting optical behaviours due to the involvement of donor–acceptor and metal–metal interactions. Notably, addition of polar solvent, hexafluoroisopropanol, cleavages intramolecular NH⋯O hydrogen bonds and thereby triggers conformational change for the molecular tweezer receptor. Consequently, molecular tweezer/guest complexation could be significantly influenced, benefiting for further construction of intelligent molecular machines and devices. Graphical abstract image
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5-Quinolinecarboxaldehyde as a precursor of luminescent boron complexes: synthesis and optical studies ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Karima Benelhadj, Pascal Retailleau, Julien Massue, Gilles Ulrich 5-Quinolinecarboxaldehyde was used as a starting synthon to engineer a series of highly luminescent boron complexes based on BODIPY dyes or on original benzimidazole or phenanthroimidazole N^N chelates. For the BODIPY series, the 5-quinoline fragment was either introduced at the meso position of the π-conjugated core via a pyrrolic condensation or at the 3,5 positions through Knoevenagel condensations. The N^N chelates were prepared with o-phenylenediamine or phenanthrenedione, respectively, followed by boron complexation. All these original complexes were characterized by structural and/or photophysical studies. The latter revealed absorption bands spanning the entire visible range and very intense emission bands upon photoexcitation. The photoluminescence quantum yields are very high, reaching up to unity, highlighting the potential use of these complexes as luminescent probes. Graphical abstract image
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An attempt to construct the C/D ring system of parkacine by intramolecular cycloaddition of azomethine ylide and alkyne ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Wenxuan Zhang, Jiming Wang, Xihuan Luo, Xiangbao Meng, Zhongjun Li Intramolecular 1,3-dipolar cycloaddition of chiral hept-6-yne-azomethine ylide was attempted to construct the C/D ring system of a lycorine-type alkaloid parkacine (3). However, the cycloaddition reactions gave C/D ring-closure product with opposite configurations at 7- and 7a-carbons, comparing with the natural product. The unexpected epimerization of phenyl substituted chiral carbon may occur through imine–enamine tautomerism before the intramolecular cycloaddition. Graphical abstract image
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Three-component domino cyclization of novel carbazole and indole fused pyrano[2,3-c]pyridine derivatives ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Wenhui Zhang, Jianqiang Wang, Jingpeng Mao, Li Hu, Xiaohua Wu, Cheng Guo A series of novel carbazole and indole fused pyrano[2,3-c]pyridine library were constructed via a three-component domino cyclization of 4-hydroxycarbazole, aromatic aldehydes, and 2-aminoprop-1-ene-1,1,3-tricarbonitrile in anhydrous ethanol using EtONa as a base under microwave irradiation. The 27 examples of the potential chemically and biomedically significant pyrano[2,3-c]pyridine derivatives were first prepared by this simple and efficient method. Moreover, this procedure lowers the number of intermediate technologic stages, reduces the energy consumption, and avoids complicated purification operations. Graphical abstract image
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A new direct synthesis of α-methylene- and α-alkylidene-β-lactams ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Marwa Hussein, Assaad Nasr El Dine, Farès Farès, Vincent Dorcet, Ali Hachem, René Grée The Kinugasa reaction applied to alkynes bearing a nucleofuge in propargylic position affords directly, and in fair yields, α-methylene- or α-alkylidene-β-lactams. Graphical abstract image
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Synthesis of fused azacycle via Overman rearrangement and ring-rearrangement metathesis as key steps ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Sambasivarao Kotha, Ongolu Ravikumar A simple and concise approach to fused tricyclic compound containing five stereogenic centers and one nitrogen atom is described starting with a readily available building block dicyclopentadiene. This route involves the Overman rearrangement and ruthenium catalyzed ring-rearrangement metathesis as key steps. Graphical abstract image
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Marinopyrones A–D, α-pyrones from marine-derived actinomycetes of the family Nocardiopsaceae ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Jihye Lee, Chulkyeong Han, Tae Gu Lee, Jungwook Chin, Hyukjae Choi, Wonjae Lee, Man Jeong Paik, Dong Hwan Won, Gyusang Jeong, Jaeyoung Ko, Yeo Joon Yoon, Sang-Jip Nam, William Fenical, Heonjoong Kang Two actinomycetes, a member of the rare halophilic genus Streptomonospora and a Nocardiopsis sp. (Nocardiopsaceae), strains CNQ-082 and CNQ-675, respectively, were isolated from marine sediments collected off shore near La Jolla, California. HPLC-UV guided fractionations of the extracts of these strains yielded marinopyrones A–D (1–4), the structures of which were elucidated by interpretation of 1D and 2D NMR and HRMS spectroscopic data. Oxidative ozonation, followed by conversion of the acid product to an α-naphthyl amide, provided the absolute configuration at the chiral center on the side-chain. Marinopyrones A–D were examined for the inhibitory activity on nitric oxide production in LPS-activated mouse macrophage cells (RAW 264.7); marinopyrone D (4) was inhibitory with an IC50 value of 13μM. To our knowledge, marinopyrones A–C are only the second reported natural products from the rare halophilic genus Streptomonospora. Graphical abstract image
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A convenient and efficient approach to synthesize negletein from baicalin ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Guihua He, Yu Gao, Cailong Li, Guolin Wu, Yazhen Li, Longrong Dong, Changcang Huang, Haijun Chen A simple two-step/one-pot and highly efficient strategy for the synthesis of negletein from naturally abundant and inexpensive baicalin has been developed. In this one-pot sequence, esterification of baicalin catalyzed by concentrated H2SO4 in methanol followed by the treatment with excess NaBH4 afforded negletein in moderate yield. This method provides an additional approach for the synthesis of negletein. Graphical abstract image
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Synthesis of acridine-1,8-dione substituted (E)-5-(3-aminoallyl)-uridine-5′-triphosphate: a new potential fluorogenic molecular probe ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Annamalai Senthilvelan, Shanmugasundaram Muthian, Gerardo Yepez, Anilkumar R. Kore The first synthesis of highly fluorescent acridine-1,8-dione dye labeled aminoallyl-uridine-5′-triphosphate is described. The coupling reaction of acridine-1,8-dione benzoic acid succinimidyl ester with aminoallyl-uridine-5′-triphosphate, followed by anion exchange purification results in the final compound with good yield and high purity. The acridine-1,8-dione benzoic acid succinimidyl ester is obtained by the reaction of acridine-1,8-dione benzoic acid with N-hydroxysuccinimide. This fluorogenic acridine-1,8-dione dye substituted uridine nucleotide has potential to generate labeled nucleic acids for molecular biology and molecular cytogenetic applications. Graphical abstract image
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Crystallization-based resolution of 1,4-benzodioxane-2-carboxylic acid enantiomers via diastereomeric 1-phenylethylamides ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Laura Fumagalli, Cristiano Bolchi, Francesco Bavo, Marco Pallavicini Unlike the diastereomeric 1-phenylethylammonium salts, the diastereomeric N-1-phenylethylamides of (S)- and (R)-1,4-benzodioxane-2-carboxylic acid show significant differences in fusibility and solubility so as to be efficiently resolved by precipitation of the less soluble diastereomer (>98%de), while chromatographic purification of the unprecipitated fraction affords the more soluble one (>99%de). Overall, 95% of the former and 80% of the latter are recovered. The hydrolysis of the two resolved amides provides the two acid enantiomers and the resolving amine in quantitative yield and with unchanged stereoisomeric purity. Graphical abstract image
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Synthesis and absolute configuration of formosusin A, a specific inhibitor of mammalian DNA polymerase β ()
Publication date: 4 May 2016 Source:Tetrahedron Letters, Volume 57, Issue 18 Author(s): Arata Yajima, Yuu Iizuka, Ryo Katsuta, Tomoo Nukada Formosusin A, a specific inhibitor of an X-family DNA polymerase (rat DNA polymerase β), was synthesized using a Sharpless asymmetric dihydroxylation as the key step for the preparation of a chiral building block. This Letter describes the first example of the total synthesis of formosusin A. The absolute configuration of the natural formosusin A was determined to be (R) from the specific rotation value. Racemization of formosusin A was observed under acidic conditions, suggesting that the reported natural product might have low optical purity. Graphical abstract image
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Editorial board ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17
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Synthesis of 3-substituted carboxylate/carboxamide flavone derivatives from 4-hydroxycoumarin, β-nitrostyrene and alcohol/amine using multicomponent reaction ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Suchandra Bhattacharjee, Abu T. Khan A wide range of 3-substituted carboxylate/carboxamide flavone derivatives were synthesized from 4-hydroxycoumarin, β-nitrostyrene and alcohol/amine using multicomponent reaction in the presence of N,N-dimethyl-4-aminopyridine (DMAP). Good yield, short reaction time, atom economy, cost effectiveness, and use of non-toxic organo-catalyst are some of the remarkable advantages of the present protocol. Graphical abstract image
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A hitherto undescribed addition of the lithium salt of dimethyl methylphosphonate to N-substituted phthalimides ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Piotr M. Zagórski, Andrzej Jóźwiak, Mieczysław W. Płotka, Dariusz Cal The hitherto unknown addition of the lithium salt of dimethyl methylphosphonate 6 to the N-substituted phthalimides 7 is described. This reaction allows the synthesis of new systems in which the phosphono group is connected to the heterocyclic skeleton of an isoindolinone at the 3-position by one methylene group. Graphical abstract image
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Theoretical studies on the conformation of large carbocyclic rings. I. 5,6,11,12,17,18-Hexahydrotribenzo[a,e,i]cyclododecane (1,2;5,6;9,10-tribenzododeca-1,5,8-triene) ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Ibon Alkorta, José Elguero Tribenzododecatriene is a simple and symmetric molecule that constitutes an excellent model for comparing structural properties both measured and computed. B3LYP/6-311++G(d,p) calculations perfectly reproduced the geometry and NMR properties of this compound in its C 2 geometry. Graphical abstract image
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Synthesis of 1-naphthaldehydes via the cascade reactions of 1-phenylpent-4-yn-2-ols promoted by iodine monochloride ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Bin Li, Nana Shen, Xuesen Fan, Xinying Zhang A novel and convenient synthesis of 1-naphthaldehydes through iodine monochloride promoted cascade reactions of 1-phenylpent-4-yn-2-ols is presented. Compared with literature procedures, this new method has advantages such as simple operation procedure, mild reaction conditions, good efficiency, and excellent regio-selectivity. Graphical abstract image
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Synthesis and properties of novel 9,10-di(naphthalen-2-yl)anthracene derivatives ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Ning Xiang, Xinghua Huang, Zhenyuan Xia, Guojian Tian, Jinhai Huang, Qiaochun Wang, Jianhua Su Three novel molecules were designed and synthesized based on a known compound 9,10-di(naphthalen-2-yl)anthracene (MADN). To broaden the π-conjugated system, three units with different electronegativity were introduced and connected to the C-2 position of MADN by vinyl unit. The Suzuki reaction, the Wittig reaction, and the Heck reaction were employed to synthesize these compounds. MADN is a well-known anthracene derivative which has been widely used as blue emitter. All these results indicate that these novel MADN derivatives could be some kind of potential materials for OLEDs. Graphical abstract image
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A novel colorimetric and OFF–ON fluorescent chemosensor based on fluorescein derivative for the detection of Fe3+ in aqueous solution and living cells ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Yan Gao, Huimin Liu, Qinglei Liu, Wei Wang A novel benzothiazole-functionalized fluorescein derivative was designed and synthesized. Sensor 1 displays highly selective and sensitive OFF–ON fluorescence response and naked-eye color change to Fe3+ in aqueous solution at pH 7.2. The mechanisms have been supported by Job’s plot evaluation, fluorescence titrations, MS, and 1H NMR spectroscopic studies. The detection limits of sensor 1 to Fe3+ were estimated to be 7.4nM. 1 exhibits low cytotoxicity and cell-membrane permeability, which makes it capable of Fe3+ bioimaging in living Hep G2 cells. Graphical abstract image
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Efficient synthesis of rottlerin and its two subunits ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Yangfeng Li, Biao Yu, Renxiao Wang Rottlerin, a natural product isolated from Mallotus philippensis, is associated with a range of biological activities. Its chemical structure is featured by two different substituted phloroglucinol units linked by a methylene group. In this study, we accomplished a total synthesis of rottlerin using phenol–aldehyde condensation as the key reaction. By our method, gram-scale preparation of the two structural subunits was achieved, and rottlerin was obtained in a longest eight linear step with 20% overall yield. Our study provides a practical solution for obtaining the sample of rottlerin in an efficient way. Graphical abstract image
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A one-pot method for the preparation of 2,5-diarylthiophene-1-oxides from arylacetylenes ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Robert W. Miller, Nicholas J. Dodge, Adam M. Dyer, Eleanor M. Fortner-Buczala, Adam C. Whalley 2,5-Diarylthiophene-1-oxides have been prepared from readily available arylacetylene precursors via zirconacyclopentadiene intermediates. The isolated yields of the desired thiophene-1-oxides are comparable to those obtained from the oxidation of thiophene derivatives while avoiding the formation of over-oxidation products. Furthermore, this route offers broader versatility than commonly used methods by providing products outfitted with electron-donating or electron-withdrawing groups with very little variation in isolated product yields. Finally, this strategy provides access to products containing functional groups that are not compatible with oxidation conditions. Graphical abstract image
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Superelectrophilic sp3 CH bond intermolecular functionalization of primary alcohols CnH2n+1OH (n=7, 8, 9) leading to new neo-alcohols with remote functional groups or new macrocyclic lactides ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Irena S. Akhrem, Djul’etta V. Avetisyan, Lyudmila V. Afanas’eva, Oleg I. Artushin, Nikolai D. Kagramanov Two new types of Csp 3–H functionalization reactions of alcohols C n H2 n +1OH (n =7–9) with the superelectrophilic complex CBr4·2AlBr3 and CO have been developed. In the presence of various nucleophiles (EtOH, i PrOH, CF3CH2OH, HCF2CF2CH2OH, furan, pyrrole, thiophene, morpholine, and anisole), the reaction furnishes new neo-alcohols with remote functional groups. In the absence of external nucleophiles, macrocyclic lactides are produced. Graphical abstract image
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Self-assemblies formed by isonicotinic acid analogues axially coordinating with zinc porphyrin via pyridyl unit: synthesis and application in dye sensitized solar cells ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Jun-Xiang Zhang, Fa-Ming Han, Jia-Cheng Liu, Ren-Zhi Li, Neng-Zhi Jin A novel zinc porphyrin ZnP bearing a 1,3,5-triazine-2,4-diamine unit has been designed and synthesized in good yields to construct axial-coordinated assemblies (denoted as ZnP–Ai, i = 1, 2, 3 and 4) with different isonicotinic acid analogues (assigned as A1, A2, A3 and A4) through zinc-to-ligand axial coordination approach. Then these assemblies were grafted onto TiO2 electrode surface to build dye sensitized solar cells. The performance of these cells also was examined. Photoelectrochemical measurements illustrate that all the assembly based cells have certain capabilities to export photocurrent. Especially, the ZnP–A2 assembly with a cyanoacrylic acid group based solar cell has the highest conversion efficiency of 0.81% with a JSC of 3.0mA/cm2, a VOC of 0.38V, and a FF of 0.71 among these assembly based solar cells. Additionally, the UV–vis absorption, fluorescence spectra, density functional theory (DFT) calculations, transmission electron microscopy (TEM) and electrochemical impedance spectra (EIS) were performed to determine the photoelectric behavior as well as morphological structure on the TiO2 surface modified by these assemblies. Graphical abstract image
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Metal-free hydration of ynamides: convenient approach to amides ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Hai Huang, Luning Tang, Yang Xi, Guangke He, Hongjun Zhu The trifluoroacetic acid (TFA) mediated hydration of ynamides was developed, which is an efficient approach for the synthesis of N-monosubstituted amides. This convenient method is effective with a wide range of substrates under room temperature condition, and the products are obtained in high to excellent yields through an easy work-up process. Graphical abstract image
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A new multi-addressable molecular switch based on a photochromic diarylethene with a thieno-imidazole unit ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Yaming Xue, Renjie Wang, Chunhong Zheng, Gang Liu, Shouzhi Pu A novel photochromic diarylethene has been synthesized using dithieno-benzo-imidazole as a functional group and perfluorodiarylethene as photon-controlled unit via a benzene linkage. The diarylethene could be used as a multi-addressable fluorescence switch upon triggering by acid/base, light, and Al3+ in acetonitrile. When stimulated by base, the absorption maximum of its closed-ring isomer was red-shifted from 560nm to 594nm with an evident color change from purple to blue. When induced by acid, the emission intensity of its open-ring isomer was enhanced by 109 fold with a notable fluorescence color change from dark to bright cyan. Moreover, its fluorescence intensity was dramatically increased when triggered by Al3+ and its emission peak was red-shifted from 460nm to 476nm due to the formation of a 1:2 metal/ligand complex. In addition, its light and metal-responsive fluorescence behavior was applied to the construction of a molecular logic circuit with three inputs and one output. Graphical abstract image
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2-Chloro-4-tetrafluorophenoxypyrimidine: a versatile reagent for C-2 prior to C-4 functionalizations ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Michael O’Donnell, Jean-Damien Charrier A novel synthetic route to 2,4-functionalized pyrimidines is reported. The approach uses 2-chloro-4-tetrafluorophenoxypyrimidine, that enables sequential palladium catalyzed functionalization at the pyrimidine C-2 position, followed by SNAr displacement with diverse amines at C-4. The broad utility of this ‘C-2 then C-4’ functionalization sequence has been demonstrated with a range of cross-coupling partners and amines. Graphical abstract image
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An improved and efficient strategy for the total synthesis of a colistin-like peptide ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Suhas Ramesh, Thavendran Govender, Hendrik G. Kruger, Fernando Albericio, Beatriz G. de la Torre Polymyxins have re-emerged as the last-line therapy for treatment against extremely multi-drug resistant Gram-negative bacteria, which pose a global threat to public health. Colistin is a polymyxin antibiotic which is effective against most Gram-negative bacteria. Herein, we report a facile and convenient synthesis of a colistin analogue. All the Dabs were protected as Boc groups except for Dab4 which was Alloc protected and used for cyclization with Thr10. The choice of Boc over other protecting groups was to enhance the solubility of the peptide. Cyclization in a volatile solvent such as DCM under very mild conditions and precipitation of the peptide using water are additional advantages of this protocol which can potentially be used for bulk production. The colistin analogue revealed good antibacterial activity in comparison to the natural version. Graphical abstract image
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Tandem vinylcyclopropane ring opening/Prins cyclization for the synthesis of 2,3-disubstituted tetrahydropyrans ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): B.V. Subba Reddy, V. Swathi, Manika Pal Bhadra, M. Kanaka Raju, A.C. Kunwar An efficient synthesis of 2,3-disubstituted tetrahydropyrans from aldehyde and cyclopropyl alkenol has been accomplished using HBF4·OEt2 as a promoter through a tandem vinylcyclopropane ring-opening/Prins cyclization. It is a convenient process to generate a structurally diverse and biologically relevant 2,3-disubstituted tetrahydropyrans in good yields with high selectivity. Graphical abstract image
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Isolation and characterization of santolinoidol, a bisabolene sesquiterpene from Achillea santolinoides subsp wilhelmsii (K. Koch) Greuter ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Layal Fahed, Marc El Beyrouthy, Naïm Ouaini, Véronique Eparvier, Didier Stien The essential oil (EO) obtained by hydrodistillation of aerial parts of Lebanese Achillea santolinoides subsp wilhelmsii (K. Koch) Greuter was analyzed by GC and GC–MS. The identity of the second major compound was uncertain. Its structure was elucidated using 1D and 2D NMR spectroscopy as well as MS data. It appeared to be a new sesquiterpene with a 1-oxa-bicyclo[5,4,0]-undecane skeleton which was named santolinoidol. The EO revealed interesting antimicrobial potential particularly against Trichophyton species, Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA) with MIC values ranging from 16 to 128μg/ml. Graphical abstract image
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Partial synthesis of 14-deoxy-14-aminotriptolide ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): El Bachir Kaloun, Christophe Long, Nicolas Molinier, Viviane Brel, Frédéric Cantagrel, Georges Massiot Triptolide is a diterpene triepoxide isolated from Tripterygium wilfordii, a Chinese medicinal plant and possessing a wealth of biological activities. In order to produce more soluble derivatives of triptolide, its 14-amino analogue was prepared. Initial attempts at its preparation using classical displacements led to rearranged compounds and success was finally met using carefully controlled Borch conditions. 14-Deoxy-14-aminotriptolide was thus prepared for the first time and it was found 10 times less cytotoxic than the parent compound. Graphical abstract image
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Tuning the strain effect to induce selectivity through intramolecular nitrene insertion into an adjacent methoxy CH bond leading to form a new benzoxazole: experimental and computational studies ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Sambasivan V. Eswaran, Divneet Kaur, Krishnendu Khamaru, Sripadi Prabhakar, T. Sony, Partha Raghunathan, Bishwajit Ganguly Pyrolysis of azido-meta-meconine yields only a single product 1D, which has been characterized spectroscopically (1H NMR, 13C NMR, HSQC, DEPT & MS). These results reveal that the fused five-member lactone ring can influence the product selectivity. The DFT calculations suggest the formation of favourable oxazolidine intermediate compared to azirine (1Z) and ketenimine (1H) intermediates. The isodesmic analysis showed that the fused lactone aryl nitrene (1N) would have more strain to form azirine (1Z) intermediate than the corresponding aryl nitrene (1M). Graphical abstract image
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Triisopropyl borate mediated N-sulfinyl imine formation ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Michael D. Visco, Jonathan T. Reeves, Maurice A. Marsini, Ivan Volchkov, Carl A. Busacca, Anita E. Mattson, Chris H. Senanayake Triisopropyl borate effects the condensation of aldehydes with sulfinamides to give N-sulfinyl imines. The reaction is amenable to 1°, 2°, and 3° alkyl aldehydes, as well as aryl, heteroaryl, and α,β-unsaturated aldehydes. In addition to tert-butanesulfinamide, the condensation is also effective with 4-toluenesulfinamide and 2,4,6-triisopropylphenylsulfinamide. This protocol proceeds under homogeneous reaction conditions and requires no post-reaction filtration of insoluble reagents or byproducts. Graphical abstract image
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Optimized synthesis of a pentafluoro-gem-diol and conversion to a CF2Br-glucopyranose through trifluoroacetate-release and halogenation ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Robert A. Hazlitt, Jinu P. John, Que-Lynn Tran, David A. Colby Pentafluoro-gem-diols are substrates that enable the synthesis of valuable difluoromethylene-containing organic molecules through the release of trifluoroacetate. Currently, only one synthetic strategy is available to assemble these important precursors. Herein, two new synthetic strategies to a complex pentafluoro-gem-diol are compared to the existing route, and an improved synthetic route has completed. Moreover, the first synthesis of a CF2Br-glucopyranose was finished by a tandem trifluoroacetate-release halogenation/cyclization protocol. Graphical abstract image
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Convenient approach to ω-aminoalkylthiophenes ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Tetiana Shvydenko, Kostiantyn Nazarenko, Kostiantyn Shvydenko, Serhii Filimonchuk, Yurii Vlasenko, Andrei Tolmachev, Aleksandr Kostyuk Starting from readily accessible cyclic enaminoesters, arylisothiocyanates and α-haloketones, a facile method for the synthesis of ω-aminoalkylthiophene hydrobromides was developed. It was shown that in the first step cyclic enaminoesters react with arylisothiocyanates exclusively at the enamine position. Upon treatment with base, free 5-aminopentylthiophenes were prepared. In the case of shorter alkyl substituents (4-aminobutyl and 3-aminopropyl) the free ω-aminoalkylthiophenes undergo intramolecular condensation of the amino and ketone groups affording novel fused heterocycles—thieno[2,3-c]azepine and thieno[2,3-c]azocine. Graphical abstract image
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Metal-free, iodine-catalyzed regioselective sulfenylation of indoles with thiols ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Shanli Yi, Meichao Li, Weimin Mo, Xinquan Hu, Baoxiang Hu, Nan Sun, Liqun Jin, Zhenlu Shen An iodine-catalyzed regioselective sulfenylation of indoles in the presence of DMSO has been presented. Various indoles can react with aryl thiols or alkyl thiols to afford their corresponding 3-sulfenylindoles in good to excellent yields. The notable features of this protocol include easy operation, metal-free reaction conditions, and excellent functional group tolerance. Graphical abstract image
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Design, syntheses and aggregation-induced emission properties of two new enlarged tetraarylethene-based luminogens ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Zhao-Ming Zhang, Fang-Fang Han, Ran Zhang, Nan Li, Zhong-Hai Ni Two new enlarged tetraarylethene-based compounds in which biphenyl and 4,5,9,10-tetrahydropyrene cores connect multiple arylethene units have been synthesized through convenient synthetic procedures. The optical properties and electrochemical properties of the two compounds have been investigated. The two compounds possess high emission efficiency in solid state. Particularly, the absolute fluorescence quantum yield of 4,5,9,10-tetrahydropyrene-cored compound in a solid film is up to 44.1%. The emissions of the two compounds in solutions are very weak but they become strong emitters in solid state or in poor solvents, showing aggregation-induced emission (AIE) characteristics. The two compounds exhibit high thermal stability with T d above 427°C and show relatively high glass transition temperature with T g above 142°C. Graphical abstract image
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On the Lewis base-promoted alkynylation of electron-deficient fluorobenzenes with trimethylsilylacetylenes ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Takanobu Sanji, Satoru Watanabe, Tomokazu Iyoda The Lewis base-promoted alkynylation of fluorobenzenes using trimethylsilylacetylenes studying the reactivity as a function of the number of fluoride groups is described. The reaction of 1-(pentafluorophenyl)- and 1-(3,4,5-trifluorophenyl)-2-phenylacetylenes and 1-(4-methoxyphenyl)-2-trimethylsilylacetylene with CsF/18-crown-6 in DMSO gave the alkynylated products in moderate to good yields with high regioselectivity under mild conditions. However, the 3,4-difluorophenyl derivative showed low reactivity. Graphical abstract image
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Electronically deficient (Rax,S,S)-F12-C3-TunePhos and its applications in asymmetric 1,4-addition reactions ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Shu-Bo Hu, Zhang-Pei Chen, Ji Zhou, Yong-Gui Zhou A novel electronically deficient chiral diphosphine ligand (Rax ,S,S)-F12-C3-TunePhos has been concisely synthesized. The electron-poor ligand features both chiral centers and chiral axis bearing fluoro-functional groups on each phosphorus phenyl ring based on C3-TunePhos backbone. The catalyst composed of this ligand and rhodium showed excellent activities and enantioselectivities in asymmetric 1,4-addition reactions of arylboronic acids to diverse α,β-unsaturated ketones with up to 99% ee. Graphical abstract image
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An improved and efficient synthesis of pinene based bipyridyldiols and bipyridine ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Ramalingam Boobalan, Chinpiao Chen An improved and efficient synthesis of pinene based two bipyridyldiols and bipyridine is reported. For the first time, the sealed tube-pressure reaction of pinene based pyridone with phosphoryl chloride produced an excellent yield (95%) of pinene based 2-chloropyridine, which renders synthesizing pinene based bipyridyldiols a highly inexpensive and high yielding process. Moreover, highly effective reaction condition was developed for homocoupling of chloropyridine with Ni(0) that afforded pinene based bipyridine in a high yield (84%). These newly demonstrated sealed tube-pressure chlorination and homocoupling reaction of chloropyridine afford extremely effect route for the synthesis of pinene based bipyridine. Graphical abstract image
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Rhodamine–naphthalene conjugate as a novel ratiometric fluorescent probe for recognition of Al3+ ()
Publication date: 27 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 17 Author(s): Jing-Can Qin, Jun Yan, Bao-dui Wang, Zheng-yin Yang In this study, a novel chemosensor (HL) for Al3+ which contains rhodamine and naphthalene moieties has been designed and synthesized. In the presence of Al3+, the receptor exhibited a strong, increasing fluorescent emission centered at 550nm at the expense of the fluorescent emission of HL centered at 520nm. We proposed that the addition of Al3+ triggered intramolecular fluorescence resonance energy transfer (FRET) from naphthalene to Rhodamine 6G. Graphical abstract image
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Editorial board ()
Publication date: 20 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 16
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A one-pot synthesis of trichloromethylated pyrimidines from trichloroacetimidamides and acetylenic esters ()
Publication date: 20 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 16 Author(s): Issa Yavari, Alaleh Malekafzali, Reza Eivazzadeh-Keihan, Stavroula Skoulika, Rahman Alivaisi A one-pot synthesis of functionalized trichloromethylated pyrimidines from the reaction of trichloroacetimidamides, generated by the addition of guanidine derivatives to trichloroacetonitrile, and acetylenic esters, in good yields is described. Graphical abstract image
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A Strecker approach to 2-substituted ethyl 5-aminothiazole-4-carboxylates ()
Publication date: 20 April 2016 Source:Tetrahedron Letters, Volume 57, Issue 16 Author(s): Ken Cheng, Andrew McClory, Whitney Walker, Jie Xu, Haiming Zhang, Remy Angelaud, Francis Gosselin A general approach to 2-substituted ethyl 5-aminothiazole-4-carboxylates is reported herein. Both aliphatic and aromatic thioamides undergo 1,2-addition to ethyl glyoxylate to give hemiaminals which, when treated with acetyl chloride, undergo elimination to the corresponding imines. Upon exposure to aqueous sodium cyanide the imines undergo a Strecker addition–cyclization reaction to provide the target heterocycles in modest to good yields over the 3-step process. Graphical abstract image
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