Tetrahedron Letters

Editorial board ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52
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Graphical Contents List ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52
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Recent advances of desymmetrization protocol applied in natural product total synthesis ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Ming Wang , Minghao Feng , Bingqing Tang , Xuefeng Jiang Desymmetrization synthesis strategy has simplified and improved the efficiency of synthesis, which attracted great attention in the past few decades. Since the strategy has been developed rapidly and got a wide range of applications in natural product total synthesis, the rules are urgent to be summarized. In this Letter, the recent developments of desymmetrization protocol in natural product total synthesis were summarized. Graphical abstract image
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The development for the synthesis of chiral acyclic nucleosides and their phosphonates ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Ming-Sheng Xie , Hong-Ying Niu , Gui-Rong Qu , Hai-Ming Guo Acyclic nucleosides and their phosphonates possess significantly antiviral and cytostatic activities. For acyclic nucleosides and their phosphonates, the introduction of a chiral group to their side chain or the absolute configuration of the chiral atom could affect their biological activities obviously. Thus, the asymmetric synthesis of chiral acyclic nucleosides and their phosphonates has received continuous attention. The previous reports mainly focus on employing the chiral pool and chiral auxiliary methods for the synthesis of chiral acyclic nucleosides and their phosphonates. In contrast, the asymmetric catalysis methods for the synthesis of acyclic nucleosides and their phosphonates are still in the beginning. This digest paper will serve to highlight the significant progress that has been made in these areas. Graphical abstract image
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Copper(II) bromide as an efficient catalyst for acetal to bisarylmethyl ether interconversion ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Rofia Mezaache , Hassina Harkat , Julie Obszynski , Abdelhamid Benkouider , Aurélien Blanc , Jean-Marc Weibel , Patrick Pale Transprotection of acetals to bis(methoxyphenyl)methyl (BMPM) ethers can be efficiently achieved in the presence of copper dibromide as catalyst in acetonitrile at room temperature. Acetals are conveniently and selectively converted to the corresponding mono-protected diol with bis(methoxyphenyl)methyl isopropyl ether (BMPMOiPr) as the reagent. This new practical reagent allows the BMPM transfer to 1,3-dioxolanes or 1,3-dioxanes under copper catalysis. The reaction conditions are also very mild and tolerant to various functional groups, including other protecting groups. Graphical abstract image
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Chemoselective deprotection of N-allylic amines using DDQ ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Pradeep Kumar , Shijo K. Cherian , Ruchi Jain , Krishanu Show A highly chemoselective and simple method for the deprotection of N-allylic amines using DDQ has been developed. The use of DDQ in dichloromethane–water provides a mild and efficient one-step deallylation of a wide variety of orthogonally protected tertiary amine derivatives. Graphical abstract image
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Synthetic studies on lycopodine: construction of hexahydrojulolidine core by intramolecular Mannich reaction ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Takanao Sato , Hirofumi Ueda , Hidetoshi Tokuyama The tricyclic core skeleton of lycopodine was constructed by the intramolecular Mannich reaction of a 12-membered cyclic amine. The concise assembly of the macrocyclic intermediate was executed by the sequential inter- and intramolecular N-alkylation of a linear diol using Ns-amide. The fully functionalized diol was prepared via Michael reaction of enone and malonate. The key Mannich reaction proceeded smoothly in the presence of silica gel to provide the tricyclic core skeleton of lycopodine. Graphical abstract image
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Effect of ionic liquids in unimolecular solvolysis reactions involving carbocationic intermediates ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Elizabeth D. Kochly , Susan Citrak , Nelius Gathondu , Gabriella Amberchan Solvolysis studies of pivaloyl triflate were performed using ionic liquid/methanol solvent mixtures. The rearranged carbocation intermediate reacts with methanol via nucleophilic attack or elimination of a proton. Relative amounts of products were determined through 1H NMR analysis. For most ionic liquids, increasing the ionic liquid:methanol ratio leads to increased yields of elimination product. Product ratios vary based on Kamlet–Taft solvatochromic parameters of hydrogen bond donating and accepting ability of the ionic liquid. Graphical abstract image
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A new and concise way to enamides by fluoroalkanosulfonyl fluoride mediated Beckmann rearrangement of α,β-unsaturated ketoximes ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Zhaohua Yan , Yun Xu , Weisheng Tian The reaction of α,β-unsaturated ketoximes with fluoroalkanosulfonyl fluorides in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) underwent the Beckmann rearrangement smoothly to afford the corresponding acid-sensitive enamides in moderate to excellent yields, which provides a new efficient method for the preparation of acid-sensitive enamides. Graphical abstract image
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Iron-catalyzed thioesterification of methylarenes with thiols in water ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Liang Wang , Jing Cao , Qun Chen , Ming-yang He An iron-catalyzed coupling reaction of methylarenes with thiols leading to thioesters has been developed. The reactions were carried out in water with tert-butyl hydroperoxide (TBHP) as the oxidant and polyoxyethanyl α-tocopheryl sebacate (PTS) as the surfactant. The reaction medium is compatible with a series of functional groups and can be reused. Graphical abstract image
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A facile synthesis of novel tricyclic 4-pyridones ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Buzhe Xu , Zhanling Cheng , Lei Fu A new and efficient synthesis of tricyclic 4-pyridone analogs through the intramolecular Heck coupling cyclization was described. This reaction features mild conditions and good functional group tolerance allowing for the preparation of several novel tricyclic 4-pyridone analogs. Graphical abstract image
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Palladium catalyzed addition of arylboronic acid or indole to nitriles: synthesis of aryl ketones ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Tuluma Das , Amarnath Chakraborty , Amitabha Sarkar Aryl ketones can be synthesized conveniently by a palladium catalyzed addition of arylboronic acid to nitriles in aqueous triflic acid. This catalytic system was extended to the addition of unprotected indoles to nitriles under a slightly modified condition to produce 3-acyl indoles in good yields. Graphical abstract image
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Three new terpenoids, sterebins O, P1, and P2, isolated from Stevia rebaudiana fermented by Saccharomyces cerevisiae ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Hitoshi Kamauchi , Tatsuhiko Kon , Kaoru Kinoshita , Kunio Takahashi , Kiyotaka Koyama The diversity of natural compounds is extensive but not unlimited. We therefore studied the feasibility of fermenting plant extracts to increase the diversity of natural compounds for use as drug candidates. Three new terpenoids, sterebins O (1), P1 (2), and P2 (3), were isolated from an extract of Stevia rebaudiana fermented by Saccharomyces cerevisiae. The structures of these compounds were established using NMR, MS, and IR methods. The absolute configuration of 1 was determined by X-ray diffraction analysis, and that of 2 and 3 from the ECD spectrum of their benzoate derivatives. These three compounds were not observed in S. rebaudiana extracts by TLC, suggesting that the compounds were generated during the fermentation process. Compounds 1, 2, and 3 all inhibited melanogenesis in theophylline-stimulated B16 melanoma cells, with 1 exhibiting the lowest IC50 value (9.8μM). The results indicate that fermentation of plant extracts may provide a route for generating many useful compounds. Graphical abstract image
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Diastereoselective synthesis of β-aminosulfones from the 1,2-addition to N-(para-methoxyphenyl) imines ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): James C. Anderson , Ian B. Campbell , Sebastien Campos , Jonathan Shannon The base-promoted 1,2-addition of alkyl phenylsulfones to N-(para-methoxyphenyl) imines was investigated as a direct route to stereochemically defined β-aminosulfones. Using n BuLi as base, 2-(phenylsulfonyl)ethylbenzene was added to a range of N-(para-methoxyphenyl) imines to give β-aminosulfone products in high yields as single anti-diastereoisomers. Other less substituted alkyl phenylsulfones were not as successful. Graphical abstract image
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Thiophosphorylated derivatives of meta- and ortho-hydroxybenzaldehydes in one-step syntheses of novel calix[4]resorcinols ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Irina R. Knyazeva , Victoria I. Matveeva , Victor V. Syakaev , Bulat M. Gabidullin , Aidar T. Gubaidullin , Margit Gruner , Wolf D. Habicher , Alexander R. Burilov , Michael A. Pudovik Thiophosphorylated derivatives of meta- and ortho-hydroxybenzaldehydes take part in one-step, acid-catalyzed condensations with resorcinol and its derivatives. As a result, new calix[4]resorcinols, which contain four 2-thioxo-1,3,2-dioxaphosphorinane fragments on the aromatic substituents of the calixarene matrix, have been synthesized. In this case, macrocyclic products are formed as rccc- (cone or boat conformation) and/or rctt- (chair conformation) diastereomers, the ratio of which depends on the structure of the starting reagents. The obtained products have been isolated and their structures determined by NMR methods and single-crystal X-ray diffraction. The spectral differences of conformational isomers of the prepared macrocycles have been demonstrated. Graphical abstract image
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Diaminophosphine oxides as preligands for Ni-catalyzed Suzuki cross-coupling reactions of aryl chlorides with arylboronic acids ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Feng Hu , Blessy N. Kumpati , Xiangyang Lei The first investigation of air- and moisture-stable diaminophosphine oxides as preligands in the Ni-catalyzed Suzuki cross-coupling reactions of aryl chlorides with arylboronic acids has been reported. The results show that under the optimized reaction conditions, the new catalytic system with a Ni(II) σ-aryl complex as precatalyst and a diaminophosphine oxide as preligand tolerates a variety of functional groups and is efficient for both electron-rich and electron-deficient aryl chlorides, though it shows higher efficiency for activated arylboronic acids than deactivated ones. Steric effects were observed for both aryl chlorides and arylboronic acids. Graphical abstract image
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Asymmetric synthesis of 2-substituted cyclic amines ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Amit A. Kudale , Prasad Anaspure , Falguni Goswami , Matthew Voss Cyanomethylenetributylphosphorane-mediated ring closure for the asymmetric synthesis of 2-substituted cyclic amines such as azetidines, pyrrolidines and a piperidine is reported. The desired stereochemistry at the 2-position was fixed using (S)-tert-butyl sulfinamide as a chiral auxiliary. Graphical abstract image
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A d-ribose-derived α-amino nitrile as a versatile intermediate for the collective synthesis of piperidine-type iminosugar C-glycosides ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Xiang-Guo Hu , A. Daryl Ariawan , Luke Hunter Iminosugar C-glycosides are valuable entities in medicinal chemistry. Herein we disclose a collective synthesis approach to such compounds, in a route that features a remarkably stable, fully characterised, ribose-derived iminium salt as a key intermediate. Addition of organometallic reagents to this key intermediate delivers a variety of iminosugar C-glycoside products in high yields and with excellent stereocontrol. Graphical abstract image
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Synthesis of febrifuginol analogues and evaluation of their biological activities ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Huong Doan Thi Mai , Giang Vo Thanh , Van Hieu Tran , Van Nam Vu , Van Loi Vu , Bich Ngan Truong , Thi Dao Phi , Van Minh Chau , Van Cuong Pham A new series of febrifuginol analogues was prepared from l-glutamic acid. An antimalarial activity evaluation against chloroquine-sensitive (T96) and chloroquine-resistant (K1) Plasmodium falciparum indicated that all the tested compounds had very strong inhibitory activity. Compounds 4 and 17b′ were inactive against KB, MCF7, HepG2 and LU1 cell lines even at a concentration of 100μM, while they exhibited significant inhibition towards P. falciparum. Comparison of the antimalarial activity and the cytotoxic properties revealed that the 2′S isomers were more active than the corresponding 2′R isomers for this series of febrifuginol analogues, indicating that the C-2′ position is critical for the biological activity of this class of compounds. Graphical abstract image
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Regioselective synthesis of multiply halogenated azaxanthones ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Wenyuan Qian , James Brown , Jian Jeffrey Chen , Yuan Cheng Four multiply halogenated azaxanthones 3, 4b, 5, and 6 were synthesized as novel core building blocks of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors. Each of these heterocycles requires a specific synthetic strategy to control not only the aza-positions, but also the regiochemistry of the fully differentiated and highly reactive halogen substituents. Graphical abstract image
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Direct α-alkylation of ketones with primary alcohols catalyzed by iridium–CNP complex ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Dawei Wang , Keyan Zhao , Piming Ma , Chongying Xu , Yuqiang Ding The α-alkylation of ketones with primary alcohols was realized by CC cross-coupling with iridium–CNP complexes as catalyst. This reaction proceeds via dehydrogenation reactions, aldol condensation, and hydrogenation using the borrowed hydrogen atoms from alcohols. The pyridyl methanols and other heterocyclic substituted methanols, especially alkyl alcohols, were also suitable for this transformation. Graphical abstract image
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A catalyst-free synthesis of α-aminophosphonates in glycerol ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Kobra Azizi , Meghdad Karimi , Akbar Heydari A simple and efficient method is described using glycerol as a solvent in the catalyst-free synthesis of α-aminophosphonates in high purity. Products are prepared by the Kabachnik–Fields reaction from amines, phosphites, and carbonyl compounds. The method does not require a toxic catalyst. Graphical abstract image
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Synthesis of three-dimensional fused and spirocyclic oxygen-containing cyclobutanone derivatives ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Sergey V. Ryabukhin , Kateryna I. Fominova , Dmitriy A. Sibgatulin , Oleksandr O. Grygorenko An approach to fused and spirocyclic oxygen-containing cyclobutanone derivatives based on ketene [2+2] cycloaddition with vinyl ethers is described. Using alicyclic chloroanhydrides as ketene sources as well as cyclic vinyl ethers in the reaction resulted in the formation of three-dimensional conformationally restricted building blocks of interest to medicinal chemistry and organic synthesis. In particular, 2-oxaspiro(bicyclo[3.2.0]heptane-7,1′-cycloalkane)-6-ones and 2-oxaspiro(bicyclo[4.2.0]octane-8,1′-cycloalkane)-6-ones were obtained. The procedure involves readily available and inexpensive starting materials and allows construction of complex molecular architectures on a large scale in a single run. Graphical abstract image
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Choline chloride based deep eutectic solvent as an efficient solvent for the benzylation of phenols ()
Publication date: 24 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 52 Author(s): Abhilash S. Singh , Suresh S. Shendage , Jayashree M. Nagarkar Deep eutectic solvents (such as the combination of urea and choline chloride) are found to be promising solvent and phase-transfer-media for benzylation of phenol. These methods avoided the complexity of multiple alkylations giving selectively O-alkylated aromatic products. Good to excellent yields of the corresponding benzyl phenyl ether were obtained. The non-toxic, biodegradable, inexpensive, and recyclable nature of DES make this protocol green and cost-effective. Graphical abstract image
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Editorial board ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51
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Graphical Contents List ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51
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Metal-free asymmetric hydrogenation and hydrosilylation catalyzed by frustrated Lewis pairs ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Xiangqing Feng , Haifeng Du The activation of H2 for the catalytic hydrogenation of unsaturated compounds is one of the most useful reactions in both academia and chemical industry, which has long been predominated by the transition-metal catalysis. However, metal-free hydrogen activation represents a formidable challenge, and has been less developed. The recent emerging chemistry of frustrated Lewis pairs (FLPs) with a combination of sterically encumbered Lewis acids and Lewis bases provides a promising approach for metal-free hydrogenation due to their amazing abilities for the challenging H2 activation. In the past several years, the hydrogenation of a wide range of unsaturated compounds using FLP catalysts has been successfully developed. Despite these advances, the corresponding asymmetric hydrogenation is just in its start-up step. Similar to the mode of HH bond activation, SiH bond can also be activated by FLPs for the hydrosilylation of ketones and imines. But its asymmetric version is also not well-solved. This Letter will outline the recent important progress of metal-free catalytic asymmetric hydrogenation and hydrosilylation using FLP catalysts. Graphical abstract image
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Selective colorimetric assay of cyanide ions using a thioamide-based probe containing phenol and pyridyl groups ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Eun Joo Song , Soojin Kim , Gyeong Jin Park , Sol Ji Park , Ye Won Choi , Cheal Kim , Jinheung Kim The selective assay of cyanide ions with a thioamide compound (HNPTU) containing phenol and pyridine as a chemosensor is reported using absorbance changes in a buffered aqueous solution (50mM HEPES, pH 7.4) containing ethanol. Upon treatment with cyanide ions, the colorless solution of HNPTU turned yellow. No significant changes were observed with other comparable anions, such as F−, Cl−, Br−, I−, and CH3COO−. The color change of HNPTU upon treatment with CN− was maintained even in the presence of the comparable monovalent anions. The complex stability constant (K a =2.6×103) for the stoichiometric 1:1 complexation of HNPTU with cyanide ions was obtained based on absorbance titrations. The interaction of HNPTU with cyanide ions was proposed to be deprotonation, as shown by NMR and Cu(II) treatment experiments. Graphical abstract image
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Efficient ZnCl2 assisted synthesis of calix[4]pyrroles catalysed by Brønsted acidic ionic liquids ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Amit Kumar Rawat , S.M.S. Chauhan A facile and efficient protocol is reported for the synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles in moderate to excellent yields by one-pot condensation of ketones and pyrrole in the presence of catalytic amount of nontoxic acidic ionic liquids. In this reaction the products were obtained in short reaction time with selectivity of regular calix[4]pyrroles. Graphical abstract image
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Design of new synthetic strategies to cyclophanes via ring-closing metathesis ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Sambasivarao Kotha , Mukesh E. Shirbhate A simple synthetic methodology to cyclophanes containing hydroxyl groups has been reported. The key steps involved here are: Grignard reaction, double Claisen rearrangement, and ring-closing metathesis. The strategy reported here is protecting group-free synthesis. Graphical abstract image
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A novel straightforward synthesis of 2,4,6-triaryl-1,3,5-triazines via copper-catalyzed cyclization of N-benzylbenzamidines ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Pradip Debnath , K.C. Majumdar A novel, straightforward method for the synthesis of 2,4,6-triaryl-1,3,5-triazines via copper-catalyzed cyclization of N-benzylbenzamidines in DMSO has been developed. Compared to other methods, the present protocol has a number of advantages such as—cost-effectiveness, avoidance of aldehydes or alcohols as reaction partners, and easy accessibility of starting materials, making it a highly practical approach to access various 2,4,6-triaryl-1,3,5-triazines. Graphical abstract image
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Synthesis of macrocycles that inhibit protein synthesis: stereochemistry and structural based studies on sanguinamide B derivatives ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Adrian L. Pietkiewicz , Hendra Wahyudi , Jeanette R. McConnell , Shelli R. McAlpine We report the synthesis of seven new sanguinamide B (SanB) analogues. Substitution of amino acids along the backbone of SanB and testing in HCT-116 colon cancer cell lines identified new biologically active SanB derivatives. These compounds establish a structure–activity relationship and show that a Cbz-lysine moiety is important for biological activity. We also identified the most effective stereochemistry at each position around the molecule. The biological activity of the macrocycle is extremely sensitive to stereochemistry and amino acid placement. Graphical abstract image Highlights
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Rapid synthesis of self-assembling 1,2-thiomannobioside glycoconjugates as potential multivalent ligands of mannose-binding lectins ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Magdolna Csávás , Tamás Demeter , Mihály Herczeg , István Timári , Katalin E. Kövér , Pál Herczegh , Anikó Borbás Among the pathogen-associated carbohydrate patterns, the Man(α1→2)Man α disaccharide motif is of particular interest because its multivalent derivatives are considered as potential antiviral or antibacterial agents through interaction with mannose-binding lectins. We present a straightforward synthesis of amphiphilic compounds containing a hydrolytically stable S-linked 1,2-mannobioside residue, a tetraethylene glycol linker to ensure water solubility and various lipophilic carriers such as a hexadecyl chain and two pyrrolidinofullerene derivatives. According to a dynamic light scattering study, the obtained amphiphiles form nanoscale aggregates in water producing multivalent presentation of the thiomannobioside residue. Graphical abstract image
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Chemoenzymatic routes to cyclopentenols: the role of protecting groups on stereo- and enantioselectivity ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Simon Specklin , Anna Dikova , Aurélien Blanc , Jean-Marc Weibel , Patrick Pale Enantiopure (R)-4-triisopropylsilyloxycyclopent-2-en-1-one was obtained through short sequences including either the enzymatic resolution of racemic cis-4-triisopropylsilyloxycyclopent-2-en-1-ol or the enzymatic desymmetrization of cis-cyclopent-2-en-1,3-diol. Alternatively, the enantiopure (S)-4-triisopropylsilyloxycyclopent-2-en-1-one was very efficiently obtained from diacetate of cis-cyclopent-2-en-1,3-diol using enzymatic desymmetrization with CAL-B. In these sequences, TIPS proved to be the best protecting group. Graphical abstract image Highlights Both (R)- and (S)-4-triisopropylsilyloxycyclopent-2-en-1-ones were prepared in enantiopure form in high yields (37–64%) from (±)-4-hydroxycyclopent-2-en-1-one, itself easily obtained from furfuryl alcohol. The chirality was introduced from either enzymatic resolution or desymmetrization. TIPS proved to be the best protecting group.
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CyanobenzeneTTF-type donors; synthesis and characterization ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Sandra Rabaça , Sandrina Oliveira , Ana Cláudia Cerdeira , Dulce Simão , Isabel Cordeiro Santos , Manuel Almeida Two cyanobenzeneTTF-type electron donors, which are also dithiolene ligand precursors, cyanobenzenedicyanoethylthiotetrathiafulvalene, (cbdc-TTF) and dicyanobenzenedicyanoethylthiotetrathiafulvalene, (dcbdc-TTF), were obtained through cross-coupling reactions with triethyl phosphite between 4,5-bis(2-cyanoethylthio)-1,3-dithiole-2-one and 4,cyanobenzene-1,3-dithiole-2-thione or dicyanobenzene-1,3-dithiole-2-thione, respectively. These reactions also yield 2,3,6,7-tetrakis(2-cyanoethylthio)-TTF and the corresponding symmetric cyanobenzene TTF derivatives dicyanodibenzenetetrathiafulvalene (dcdb-TTF) and tetracyanodibenzotetrathiafulvalene (TCN-DBTTF) resulting from the self-coupling reactions of the ketone and the thiones. Compound dcdb-TTF was also synthesized by homo-coupling reaction of the cyanobenzene-1,3-dithiole-2-ketone with triethyl phosphite. These compounds were characterized namely by single crystal X-ray diffraction and cyclic voltammetry. Graphical abstract image
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A new diketopyrrolopyrrole-based near-infrared (NIR) fluorescent biosensor for BSA detection and AIE-assisted bioimaging ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Yandi Hang , Lin Yang , Yi Qu , Jianli Hua A new near-infrared fluorophore (DPPAM) based on diketopyrrolopyrrole was developed as bioprobe and cell stain. This bioprobe is shown to be ‘turn-on’ response for BSA with high sensitivity and NIR emission ranged from 600 to 850nm. AIE-assisted bioimaging also exhibited the obvious NIR signals in some special region where the dye-aggregates attached. Graphical abstract image
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Diels–Alder reactions of five-membered heterocycles containing one heteroatom ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Xiaoyuan Ding , Son T. Nguyen , John D. Williams , Norton P. Peet Diels–Alder reactions of five-membered heterocycles containing one heteroatom with an N-arylmaleimide were studied. Cycloaddition of 2,5-dimethylfuran (4) with 2-(4-methylphenyl)maleimide (3) in toluene at 60°C gave bicyclic adduct 5. Cycloadditions of 3 with 2,5-dimethylthiophene (11) and 1,2,5-trimethylpyrrole (14) were also studied. Interestingly, the bicyclic compound 5 cleanly rearranged, with loss of water, when treated with p-toluenesulfonic acid in toluene at 80°C to give 4,7-dimethyl-2-p-tolylisoindoline-1,3-dione (6). Graphical abstract image
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Beyond Achmatowicz reaction: DDQ-mediated chemo- and stereoconvergent domino-one pot cyclization/rearrangement of bis-thioenol ether-containing chiral building blocks ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Annalisa Guaragna , Antonio Dell’Isola , Stefano D’Errico , Giovanni Palumbo , Daniele D’Alonzo A highly convergent multistep process incorporating an aza-Achmatowicz rearrangement has been described, selectively providing enantiomerically pure bicyclic (dihydro)furans 9 and 18 as well as the tricyclic dihydropyridinone 23 from acyclic starting materials after up to eight sequential synthetic transformations in one step. Graphical abstract image
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Bodipy-ruthenium(II) tris-bipyridyl dyads for homogeneous photochemical oxidations ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Pau Farràs , Andrew C. Benniston Two Bodipy-ruthenium(II) tris-bipyridyl dyads were synthesized for use as sensitizers in photochemical oxidation reactions of organic substrates. The synthetic strategy involved the use of a simple ‘click’ CuAAC reaction to link a Bodipy subunit with an organometallic ruthenium(II) tris-bipyridyl complex. The linking triazole bridge was used to minimize electronic coupling between the two subunits. The dyads showed improved performance on organic substrate photo-oxidation reactions compared to the control compound without the Bodipy moiety. Graphical abstract image
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Optimised synthesis of diamino-triazinylmethyl benzoates as inhibitors of Rad6B ubiquitin conjugating enzyme ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Hend Kothayer , Matteo Morelli , Ghali Brahemi , Abdalla A. Elshanawani , Mansour E. Abu Kull , Osama I. El-Sabbagh , Malathy P.V. Shekhar , Andrew D. Westwell Recently, we have identified the first inhibitors of Rad6B, an E2 enzyme essential for post-replication DNA repair and a potential new drug target for the treatment of breast cancer. We report two newly optimised synthetic routes to our [4-amino-6-(phenylamino)-1,3,5-triazin-2-yl]methyl 4-nitrobenzoate target compounds TZ8 and TZ9 with general applicability for further structure–activity relationship studies around this pharmacophore. The key step involved the condensation/cyclisation between phenylbiguanide and either ethyl bromoacetate or dimethyloxalate in good yield. Graphical abstract image
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An unprecedented rearrangement of a 1,1-diprotected hydrazine derivative. Structure revision of a catalyst-containing by-product ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Ulf Ragnarsson , Leif Grehn , Tõnis Pehk Treatment of 1-Boc-1-tosyl-hydrazine with 1,1,3,3-tetramethylguanidine (TMG) gave rise to two products, one containing and the other not containing TMG. The latter was identified as 1-Boc-2-tosyl-hydrazine. This rearrangement provided useful insight into the nature of the first product that had previously been isolated and assigned an incorrect tentative structure. To rationalize the results a plausible mechanism via a common intermediate, involving TMG as a nucleophilic catalyst is proposed. A simpler procedure for the preparation of the starting material is also presented. Graphical abstract image
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A facile synthesis of (carbazolyl)formamidines ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Ramu Meesala , Ahmad Saifuddin Mohamad Arshad , Mohd Nizam Mordi , Sharif Mahsufi Mansor The reactions of N-(carbazol-3-yl)acetamides with N,N-dimethylformamide in the presence of phosphorus oxychloride (POCl3) at 90°C gave the corresponding (carbazol-3-yl)formamidines in good yields. The method is compatible with a variety of functional groups. Graphical abstract image
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‘Green’ synthesis of 1,4-disubstituted 5-iodo-1,2,3-triazoles under neat conditions, and an efficient approach of construction of 1,4,5-trisubstituted 1,2,3-triazoles in one pot ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Dong Wang , Si Chen , Baohua Chen An environmentally friendly and efficient method for synthesis of 1,4-disubstituted 5-iodo-1,2,3-triazoles through [Cu(phen)(PPh3)2]NO3-catalyzed cycloaddition of organic azides and iodoalkynes under solvent-free conditions was developed. Based on this, a one-pot method for the synthesis of fully substituted 1,2,3-triazoles via cycloaddition/Suzuki reactions was also demonstrated in this report. Graphical abstract image
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Effect of Lewis acids and low temperature initiators on the allyl transfer reaction involving phthalimido-N-oxyl radical ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Shradha Patil , Liang Chen , James M. Tanko Previously, we reported allyl transfer reactions of allyl bromide and allyl phthalimido-N-oxyl substrates with hydrocarbons that result in CC bond formation. In both cases, efficient chain transfer processes along with high reaction yields were observed. Since PINO chemistry leads to an environmentally friendly method of hydrocarbon functionalization, additional studies were performed in order to improve the process. To expand the utility of this reaction, we carried out experiments to optimize reaction conditions and tested the effect of Lewis acids and low temperature initiators. Although allyl-PINO substrates reacted slightly slower than the bromides, the reactions were cleaner with little or noside products. The chain lengths for these reactions were compromised at lower temperatures, attributable to the high activation energy required for the hydrogen atom abstraction by PINO . The addition of a Lewis acid catalyst (AlCl3) improves the product yield and reaction rate, possibly due to the formation of a PINO /AlCl3 complex which lowers the activation energy for hydrogen abstraction step. Graphical abstract image Highlights
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A method for the cyanation of alkenes using nitromethane as a source of cyano group mediated by proton-exchanged montmorillonite ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Ken Motokura , Kenta Matsunaga , Akimitsu Miyaji , Sho Yamaguchi , Toshihide Baba A novel method for the cyanation of alkenes using nitromethane as a source of the cyano group is described. H+-montmorillonite mediates the cyanation through the in situ formation of trimethylsilanecarbonitrile oxide from nitromethane and allylsilane, followed by 1,3-dipolar cycloaddition and subsequent rearrangement to afford the corresponding nitriles. Graphical abstract image
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Simple and practical method for selective acylation of primary hydroxy group catalyzed by N-methyl-2-phenylimidazole (Ph-NMI) or 2-phenylimidazo[2,1-b]benzothiazoles (Ph-IBT) ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Kouta Ibe , Yu-suke Hasegawa , Misuzu Shibuno , Tsukasa Shishido , Yuzo Sakai , Yu Kosaki , Keisuke Susa , Sentaro Okamoto N-Methyl-2-phenylimidazole (Ph-NMI) and 2-phenylimidazo[2,1-b]benzothiazoles (Ph-IBT) catalyzed selective acylation of primary alcohols using acid anhydrides. The Ph-NMI- or Ph-IBT-catalyzed reaction using (PhCO)2O as an acylating agent could particularly acylate the primary hydroxy group of 1,n-diols (n ⩾3) with a high, synthetically useful selectivity. Graphical abstract image
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BF3 etherate-mediated microwave-assisted facile synthesis of thiopyrano[2,3-b]indol-2-one ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Mukund Jha , Connor Davis , Julia Fazzari , Mario Vitali A facile synthesis of indole annulated 2H-thiopyran-2-ones has been developed by condensation of indoline-2-thiones with acetoacetic esters in the presence of borontrifluoride etherate (BF3 etherate) using microwave irradiation. This one-step operationally simple methodology leads to thiopyrano[2,3-b]indol-2-ones in good yields. Graphical abstract image
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Signaling of chloramine: a fluorescent probe for trichloroisocyanuric acid based on deoximation of a coumarin oxime ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Seul Ki Lee , Myung Gil Choi , Suk-Kyu Chang A new chloramine signaling probe, based on a coumarin oxime, was developed. The coumarin oxime 1 exhibited efficient off–on type fluorescent signaling behavior toward trichloroisocyanuric acid (TCCA) in an aqueous acetonitrile solution. The signaling is due to the TCCA-assisted transformation of the oxime function to its carbonyl analogue. The presence of common metal ions and anions did not interfere with the TCCA signaling of this probe. Probe 1 was found to be useful for the sensitive determination of the concentration of the practical oxidant TCCA in an aqueous environment, with a detection limit of 7.58×10−7 M. Graphical abstract image
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Biotransformation of aromatic ketones and ketoesters with the non-conventional yeast Pichia glucozyma ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Martina Letizia Contente , Francesco Molinari , Paolo Zambelli , Valerio De Vitis , Raffaella Gandolfi , Andrea Pinto , Diego Romano The non-conventional yeast Pichia glucozyma CBS 5766 has been used for the biotransformation of different aromatic ketones and ketoesters. The growth and biotransformation conditions were optimised for the reduction of acetophenone and under optimised conditions, propiophenone, butyrophenone and valerophenone were reduced to the corresponding (S)-alcohols with high yields and enantioselectivity. Ketoreductase(s) of Pichia glucozyma showed high catalytic activities also towards aromatic β- and γ-ketoesters, being often competitive with esterase(s). These concurrent activities allowed for the preparation of hydroxyesters, hydroxyacids and lactones often in a very selective manner. Graphical abstract image Highlights
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Synthesis of a novel methylene-bridged biscarbazole derivative and evaluation of its DNA and nucleotide binding properties ()
Publication date: 17 December 2014 Source:Tetrahedron Letters, Volume 55, Issue 51 Author(s): Gang Li , Xue Zhou , Peng Yang , Yong Jian , Tuo Deng , Hongyan Shen , Ying Bao The synthesis of a novel methylene-bridged biscarbazole derivative 1 was described and the possible mechanism for its unexpectedly synthesized intermediate, compound A, was postulated. The binding properties of 1 to both Ct-DNA and nucleotides were investigated via fluorescent and UV–Vis spectra. The spectral investigations illustrated that this binary carbazole exhibited higher binding abilities to both Ct-DNA and nucleotides than its monomeric form, owing to the structurally flexible nature of double carbazole moieties fine-tuned by this non rigid methylene-linkage. Graphical abstract image Highlights
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