Tetrahedron Letters

Editorial board ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28
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Pd/phenanthroline-catalyzed arylative cyclization of o-(1-alkynyl)thioanisoles: synthesis of 3-arylated benzo[b]thiophenes ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Takayuki Yamauchi, Fumitoshi Shibahara, Toshiaki Murai The arylative cyclization of o-(1-alkynyl)thioanisoles with aryl iodides in the presence of catalytic amounts of [Pd(phen)2][PF6]2 resulted in the efficient formation of 3-arylated benzo[b]thiophenes, and a range of aryl iodides with electron-donating or -withdrawing groups could be used. While this reaction proceeded in the presence of aromatic and aliphatic groups on the terminal alkynyl carbon atom, silyl and alkoxycarbonyl groups hampered the reaction. Furthermore, this method could be extended to the synthesis of 3-arylated indoles from N,N-dimethyl-o-(1-alkynyl)aniline. All these reactions proceeded smoothly via cleavage of the carbon–heteroatom bond. In addition to the desired cyclization products, the use of a o-(hydroxypropyl)phenylmethyl substituent on the sulfur atom afforded isochroman, which should be formed by the intramolecular attack of a hydroxy group onto the benzylic carbon atom. Graphical abstract image
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Synthesis of 8-alkoxy-6-alkylamino-2-alkylthiopurine nucleosides with a straightforward multiple-functionalization strategy ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Hongguang Du, Xiaoyang Sun, Mingwu Yu, Miao Tian, Shunlai Li, Zhiqian Wang A straight forward strategy to synthesize purine nucleosides with multiple functionalization on 2-, 6-, and 8-positions has been developed successfully, which provides a series of 8-alkoxy-6-alkylamino-2-alkylthiopurine nucleosides in moderate to good yields for further biological and medical activity screening. Graphical abstract image
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A novel stereoselective [8+2] double cycloaddition route to hydronaphthalene ring systems ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Weijiang Ying, Lei Zhang, Paul A. Wiget, James W. Herndon Substituted hydronaphthalenes where each of the ten carbons of the two-ring system contains a functionality were obtained through a tandem [8+2] cycloaddition and base-catalyzed rearrangement process using dienylfurans and electron-deficient alkynes. If the [8+2] process is conducted under solvent-free conditions the process could be conducted in a single reaction flask without isolation of the chromatographically sensitive [8+2] cycloadducts. A mechanism involving base catalyzed alkene positional isomerization followed by disrotatory electrocyclic ring closure was proposed for the key reaction step that converts [8+2] cycloadducts to hydronaphthalenes. The products undergo selective ring opening–isomerization processes upon treatment with Lewis acids. Graphical abstract image
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Simple Brønsted acid catalyzed C–H functionalization: efficient access to poly-substituted pyridines ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Shujun Lai, Xuwen Ren, Jinzhong Zhao, Zhuo Tang, Guangxun Li An exceptionally simple and environmentally friendly methodology has been developed for directly functionalizing the benzylic C–H bond of the poly-substituted pyridines with aromatic imines. Simple Brønsted acid catalysts including salicylic acid and TsOH were successfully employed. Different types of poly-substituted pyridines could be efficiently obtained with moderate yields. Traditional ways to such types of pyridines involved the aromatization of the corresponding Hantzsch 1,4-dihydropyridines, while this method greatly simplified the synthetic procedures. Graphical abstract image
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The reductive cleavage of picolinic amides ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Daniel H. O’ Donovan, Claudia De Fusco, David R. Spring Treatment of picolinic amides with excess zinc in aqueous hydrochloric acid at room temperature affords the corresponding amines in good to excellent yields. The mild reaction conditions exhibit useful functional group tolerance and facilitate the application of the picolinic amide moiety as a protecting group which can be easily introduced and selectively removed. Graphical abstract image
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Transition metal free intramolecular approach for the synthesis of cyclopenta[b]chromene derivatives from phenol substituted fulvene derived azabicyclic olefins ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Ajesh Vijayan, T.V. Baiju, Sunil Varughese, K.V. Radhakrishnan A facile route towards the synthesis of cyclopentene fused chromene derivatives from strained phenol substituted fulvene derived bicyclic hydrazines is described. The reaction is proceeding through base catalyzed sequential intramolecular ring opening and ring closure of azabicyclic olefins. The transition metal free method provides an easy access to biologically relevant fused chromene ring system under relatively mild reaction conditions. Graphical abstract image
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Selective and effective rotation mode of copillar[5]arene by mono-functionalizing bulky substituent ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Lu-Zhi Liu, Zhong-Ze Hua, Wen-Gui Duan, Hong-Fei Huang, Yan Huang, Gui-Shan Lin, Bo Cen Two types of copillar[5]arenes bearing mono-functionalized bulky substituents such as phenyl and naphthyl groups were synthesized and their conformational characteristics were studied by 1H NMR spectroscopy. Their rotation mode can be induced and controlled by the bulky substituents. The OCH3 groups on phenolic units, the same side as the bulky substituent, were rotating regularly in the mode of OR-opposite-the-annulus rotation while the mode of OR-through-the-annulus was seen for the other OCH3 groups on the other side. Furthermore, their excellent binding properties with 1,4-dibromobutane(DBB) can be maintained as the fully symmetrical pillar[5]arenes. Graphical abstract image
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Direct electrophilic trifluoromethylthiolation of N-benzyl indoles using AgSCF3 ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Lan Ma, Xiu-Fen Cheng, Yan Li, Xi-Sheng Wang A novel electrophilic trifluoromethylthiolation reaction system has been developed with AgSCF3 used directly as the SCF3 source, in the presence of KI/K2S2O8/I2. Various N-benzylindoles have been trifluoromethylthiolated successfully with this system, and the mechanism of investigation showed an electrophilic reagent was generated in situ. Graphical abstract image
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Synthesis of a novel archaeal tetraether-type lipid containing a diorthoester group as a helper lipid for gene delivery ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Julie Barbeau, Nawal Belmadi, Tristan Montier, Tony Le Gall, Sylvain Dalençon, Loïc Lemiègre, Thierry Benvegnu As an alternative to recombinant virus, synthetic carriers are widely developed for providing efficient and safe DNA delivery. To reach the nucleus where nucleic acid (NA) constructs are transcripted, chemical complexes have to overcome serious cellular traps such as endosomal escape and intracellular trafficking. Here, the design and the multi-step synthesis of a stabilizing tetraether lipid analogue of archaeal counterparts containing a diorthoester moiety in the middle of the bridging chain were described. The key step involved a double coupling reaction between two diether alcohols and a diketene acetal. Under aqueous acidic conditions, the diorthoester function of the tetraether lipid can be hydrolysed to yield two monopolar diether lipids. Applied to gene delivery in association with a cationic lipid, this new helper bipolar tetraether lipid led to lipid–DNA complexes with sizes and potential zeta values depending on the charge ratios (+/−). In addition, preliminary in vitro transfection assays supported the interest of these novel bipolar lipid-based lipoplex formulations compared to standard Lipofectamine-based formulations. Graphical abstract image
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Metal-free synthesis of highly substituted quinolines under mild conditions ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Rakesh Natarajan, Peruparambil A. Unnikrishnan, Sandhya Radhamani, John P. Rappai, Sreedharan Prathapan Starting from easily accessible nitrones and acetylenes, a simple, metal free synthesis of substituted quinolines under mild conditions with high atom efficiency has been developed. Our method is flexible enough to introduce substituents regiospecifically at the 2,3,4,6,8-positions of the quinoline product. Graphical abstract image
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Syn-selective nitro-Michael addition of furanones to β,β-disubstituted nitroalkenes catalyzed by epi-quinine derivatives ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Tohru Sekikawa, Hayato Kitaura, Takayuki Kitaguchi, Tatsuya Minami, Yasuo Hatanaka Epi-quinine-catalyzed asymmetric nitro-Michael addition of furanones to β,β,-disubstituted nitroalkenes is described. The reaction proceeded smoothly with 1–5mol% loadings of epi-quinine catalysts at room temperature, giving the corresponding Michael adducts in high yields (72–93%) with extremely high diastereo- and enantioselectivities (>98/2dr, syn major; 95–99% ee). This reaction provides an effective and straightforward method for constructing all-carbon quaternary stereogenic centers adjacent to oxygen-containing quaternary stereogenic centers. Graphical abstract image
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Palladium-catalyzed enantioselective hydrophosphination of enones for the synthesis of chiral P,N-compounds ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Yu-Chuan Song, Guo-Fa Dai, Fanhua Xiao, Wei-Liang Duan We developed a method that involved an asymmetric conjugate addition of secondary phosphines to α,β-unsaturated enones bearing β-2-pyridyl substituents catalyzed by a PCP pincer–Pd complex. The technique was established for the preparation of chiral P,N-compounds in excellent enantioselectivity (up to 99% ee) under mild conditions. Graphical abstract image
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One-pot three component synthesis of 3,5-disubstituted 2,6-dicyanoaniline derivatives using 4-dimethylaminopyridine (DMAP) as a catalyst ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Suchandra Bhattacharjee, Abu T. Khan An efficient synthetic protocol was devised for the synthesis of 3,5-disubstituted 2,6-dicyanoaniline from malononitrile, aldehydes, and β-nitro-olefins by using N,N-dimethyl-4-aminopyridine (DMAP) as a nucleophilic catalyst. The important aspects of the present methodology are: use of non-toxic organo-catalyst, shorter reaction time, compatibility with wide range of substrates, and good yields. Graphical abstract image
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A new cyclohexapeptide, penitropeptide and a new polyketide, penitropone from the endophytic fungus Penicillium tropicum ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Yanbo Zeng, Hao Wang, Ramsay S.T. Kamdem, Raha S. Orfali, Haofu Dai, Gamall Makhloufi, Christoph Janiak, Zhen Liu, Peter Proksch The first chemical investigation of the endophytic fungus Penicillium tropicum isolated from leaves of Sapium ellipticum afforded a new cyclohexapeptide, penitropeptide (1), and a new polyketide, penitropone (2), in addition to two known compounds, 6-hydroxy-8-methoxy-3S,5-dimethyl-3,4-isocoumarin (3) and adametizine B (4). Their structures were unambiguously elucidated on the basis of 1D and 2D NMR spectroscopy as well as mass spectrometry, and by comparison with the literature. The absolute configurations of these two new compounds 1 and 2 were determined by Marfey’s method and X-ray single crystal diffraction, respectively. All isolated compounds were tested for their cytotoxic and antibacterial activities. However, none of them showed significant activity. Graphical abstract image
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Reductive N-methylation of amines with calcium hydride and Pd/C catalyst ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Carole Guyon, Marie-Christine Duclos, Estelle Métay, Marc Lemaire The methylation of amines by paraformaldehyde in the presence of calcium hydride as a source of hydrogen and palladium on charcoal as catalyst was studied. Depending on the quantity of paraformaldehyde, monomethylated and dimethylated amines were selectively and efficiently prepared in one pot with good yields. Graphical abstract image
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Synthesis of 6-aryl/heteroaryl-4-oxo-4H-chromene-2-carboxylic ethyl ester derivatives ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Carlos Fernandes, Pedro Soares, Alexandra Gaspar, Daniel Martins, Ligia R. Gomes, John N. Low, Fernanda Borges The development of new chemical entities represents an important challenge in pharmaceutical industry, being the use of privileged scaffolds for library design and drug discovery a valuable approach. Among the panoply of privileged structures, our research group has focused its attention on the chromone (4H-benzopyran-4-one) scaffold due to its chemical versatility and ability to bind to multiple targets. With this endeavour we report an expedite two-step procedure for the synthesis of novel 6-aryl/heteroaryl-4-oxo-4H-chromene-2-carboxylic ethyl ester. The new chromones were synthesized by a C–C Suzuki cross-coupling microwave-assisted reaction, using Pd(OAc)2 as a catalyst, and a classic Claisen condensation followed by an intramolecular cyclization process. Graphical abstract image
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Systematic synthesis, comparative studies of the optical properties, and the ICT-based sensor properties of a series of 2,4,6-tri(5-aryl-2-thienyl)pyrimidines with the D–π–A system ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Hiroki Muraoka, Takumi Obara, Satoshi Ogawa A series of 2,4,6-tri(5-aryl-2-thienyl)pyrimidines with a star-shaped D–π–A system, which have an electron deficient pyrimidine core (A) and three donor type aryl groups (D) linked by a thiophene spacer (π-spacer), were designed and systematically synthesized. Through the characterization of the molecules by UV–vis absorption and fluorescence spectroscopies, we revealed that the molecules possess distinct absorption and emission wavelengths controlled by the donor effect of the terminal aryl groups. Interestingly, 2,4,6-tris(5-p-N,N-dibutylaminophenyl-2-thienyl)pyrimidine was found to exhibit strong fluorosolvatochromic properties and a proton-sensibility based on its intramolecular charge transfer (ICT) and basic characteristics, which could allow its use as a polarity or proton sensor. Graphical abstract image
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One-pot sequential functionalizations of meso-tetrathienylporphyrins via Heck–Mizoroki cross-coupling reactions ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Maria C. Donatoni, Ygor W. Vieira, Timothy J. Brocksom, Adriano C. Rabelo, Edson R. Leite, Kleber T. de Oliveira Synthesis and sequential functionalizations of a new meso-tetraiodo(thien-2-yl)porphyrin and its Ni(II) derivative are described. The reactions for the preparation of these new porphyrins were optimized. Subsequently, four successive one-pot Heck–Mizoroki cross-coupling reactions were studied using two acrylates and varied reaction conditions. We describe an optimized protocol for the preparation of highly conjugated thienylporphyrins with the potential to be used as dyes in solar cell devices as demonstrated in our preliminary studies. Graphical abstract image
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A new synthetic strategy to 2,3-diallyl-1,4-quinones via one-pot double Claisen rearrangement and retro Diels–Alder reaction ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Sambasivarao Kotha, Rama Gunta A simple and an efficient synthetic strategy to 2,3-diallyl-1,4-quinone derivatives via a highly reliable and 100% atom economic reactions such as Diels–Alder (DA) reaction, Claisen rearrangement (CR), and retro Diels–Alder (rDA) reaction as key steps is reported. Graphical abstract image
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Investigate cleavage of β-O-4 linkage in lignin model compounds by aerobic oxidation of Cα and Cγ hydroxyl groups ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Nikhil D. Patil, Ning Yan The selective cleavage of common linkages in lignin polymers is a promising approach to generate valuable aromatic hydrocarbons. Herein, we found that on oxidation of Cα and Cγ hydroxyl groups in β-O-4 lignin model compounds with TEMPO catalyst resulted in the formation of 1,3-dicarbonyl TEMPO adduct. These oxidized products readily underwent fragmentation at Cα–Cβ bond in the presence of a catalytic amount of acid to generate corresponding carboxylic acid and phenol monomers. Graphical abstract image
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[bmim(SO3H)][OTf]/[bmim][X] and Zn(NTf2)2/[bmim][X] (X=PF6 and BF4); efficient catalytic systems for the synthesis of tetrahydropyrimidin-ones (-thiones) via the Biginelli reaction ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Hemantkumar M. Savanur, Rajesh G. Kalkhambkar, Gopalakrishnan Aridoss, Kenneth K. Laali A facile, high yielding, and simple method for the synthesis of a library of dihydropyrimidinones (and -thiones) via the one-pot Biginelli reaction of aldehydes is reported. The method employs the Brønsted acidic IL [bmim(SO3H][OTf] or Zn(NTf2)2 as catalyst along with the readily available imidazolium-ILs as solvent, and exhibits good potential for the recycling and reuse of the IL solvent. Graphical abstract image
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Synthesis of 3-substituted indolizidines from amino-ynones derivatives ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Huy-Dinh Vu, Jacques Renault, Thierry Roisnel, Nicolas Gouault, Philippe Uriac Two types of indolizidine derivatives can be synthesized from amino-ynones. In the presence of methanesulfonic acid, Meyer–Schuster rearrangement furnished vinylogues of indolizidin-3-ones whereas treatment with zinc chloride gave stable 3-alkynyl-1,5,6,7,8,8a-hexahydroindolizine-zinc complexes that were reduced to 3-alkynylindolizidines. Graphical abstract image
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A highly selective 7-hydroxy-3-methyl-benzoxazinone based fluorescent probe for instant detection of thiophenols in environmental samples ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Ruibing An, Peng Wei, Datong Zhang, Na Su A new 7-hydroxy-3-methyl-benzoxazinone based fluorescent probe for thiophenols has been designed and synthesized. The probe displays highly selective and sensitive detection to thiophenols over other common analytes with instant response and remarkable large Stokes shift. It’s noteworthy that biothiols, aliphatic thiols, and reducing anions do not perturb the sensing of thiophenols. The limit of detection of the probe was calculated as low as 24nM for thiophenols. Finally, the utility of probe was illustrated by the detection of thiophenol in real environmental water samples. Graphical abstract image
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Conformationally locked chromophores of CFP and Sirius protein ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Nadezhda S. Baleeva, Aleksandra S. Tsarkova, Mikhail S. Baranov Recent works have demonstrated the potential of fluorescent protein chromophores as useful dyes with unique photophysical properties. Herein, we report the synthesis of two novel highly fluorescent dyes based on conformationally locked chromophores of the fluorescent proteins CFP and Sirius. These novel synthetic dyes demonstrate high fluorescence quantum yields and pH-independence in the physiological pH range, making them promising molecular tools for a broad range of fluorescent labeling applications. Graphical abstract image
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Novel synthesis of physovenine and physostigmine analogs ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): C.H. Wang, S. Alluri, G. Nikogosyan, C. DeCarlo, C. Monteiro, G. Mabagos, H.H. Feng, A.R. White, M. Bartolini, V. Andrisano, L.K. Zhang, A.K. Ganguly This Letter describes a versatile synthetic approach to prepare physovenine and physostigmine analogs. A series of analogs were synthesized and evaluated for cholinesterase inhibition activities, including human acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) from human serum. Graphical abstract image
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Formal [4+2] cycloaddition of quinolines, pyridines, and isoquinolines with 3-ethoxycyclobutanones ()
Publication date: 6 July 2016 Source:Tetrahedron Letters, Volume 57, Issues 27–28 Author(s): Tatsuo Onnagawa, Yusuke Shima, Tomoyuki Yoshimura, Jun-ichi Matsuo 3-Ethoxycyclobutanones reacted with pyridines, quinolines, and isoquinolines to give the corresponding formal [4+2] cycloadducts, 9a-hydro-2H-quinolizin-2-one derivatives, by using Me3SiOTf in acetonitrile. Cycloaddition of 3-ethoxy-2-monoalkylcyclobutanones to 5-nitroquinoline or 4-cyanopyridine proceeded stereoselectively. Graphical abstract image
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Editorial board ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26
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The synthesis and biological evaluation of unsymmetrical 2,2-di(1H-indol-3-yl)-N-phenylacetamide derivatives ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Ren-Jun Li, Yan Zhou, Yang Zheng, Li Hai, Yong Wu A mild and highly efficient method has been developed for the synthesis of unsymmetrical 2,2-di(1H-indol-3-yl)-N-phenylacetamide derivatives by the regioselective Friedel–Crafts alkylation of 2-hydroxy-2-(1H-indol-3-yl)-N-phenylacetamide derivatives with various indoles catalyzed by AlCl3 at room temperature in a short reaction time in high yields (up to 96%). All these compounds were screened for their antiproliferative activity against human colorectal carcinoma HCT116 cell line. The preliminary biological study showed that some of them exhibited moderate to good antiproliferative activity in vitro. Especially, compound 3e exerted the most powerful antiproliferative activity even better than the positive control MDM-2/p53 antagonist Nutlin-3a. Graphical abstract image
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A new method for the synthesis of pyrazolidines ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Faryal Chaudhry, Benson M. Kariuki, David W. Knight Fully protected pyrazolidines can be readily obtained by acid-catalysed cyclisations of the corresponding allylic hydrazines by carbenium ion generation using concentrated sulfuric acid in dichloromethane. Graphical abstract image
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I2–DMSO promoted metal free oxidative cyclization for the synthesis of substituted Indoles and pyrroles ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Addada Ramakrishnam Raju, Regalla Venkata Reddy, Vajja Mallikarjuna Rao, Vema Venkata Naresh, Anna Venkateswara Rao A series of di substituted indole and tri substituted pyrrole derivatives were synthesized efficiently by using I2/K2CO3 in DMSO. The novel synthesis method offers the advantage of mild reaction conditions, operational simplicity, higher yields. The method is functional group tolerant and provides quick access to medicinally significant compounds in moderate to high yields. Graphical abstract image
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(1R,6R)-2,2,6-Trimethyl-3-oxabicyclo[4.2.0]octan-4-one, a new monoterpene lactone produced by males of the cocoa borer Conotrachelus humeropictus (Col.: Curculionidae) ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Daiane Szczerbowski, Gabriela G. Torrens, Mauro A.C.M. Rodrigues, Olzeno Trevisan, Sandra M.S. Gomes, Armin Tröger, Kenji Mori, Wittko Francke, Paulo H.G. Zarbin The cocoa weevil Conotrachelus humeropictus is an economically most important pest on cocoa (Theobroma cacao) and cupuaçu (Theobroma grandiflorum) cultures. Knowledge on the pheromone system of this insect is prerequisite for the development of an integrated pest management system. GC/MS-analysis of headspace volatiles revealed the presence of three male specific compounds, which were identified to be (1R,2S)-grandisol, (1R,2S)-grandisoic acid, and the new bicyclic terpene lactone (1R,6R)-2,2,6-trimethyl-3-oxabicyclo[4.2.0]octan-4-one, which we term grandisolide. Graphical abstract image
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A practical synthesis of N-alkyl- and N,N′-dialkyl-polyamines ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Travis J. Haussener, Paul R. Sebahar, Hariprasada R. Kanna Reddy, Dustin L. Williams, Ryan E. Looper A variety of polyamines have been synthesized from their corresponding amino alcohols through a 3-step process. The synthesis predicates that the most likely impurities are of higher molecular weight and that distillation is effective at producing highly pure materials. This sequence is scalable, requires no protecting groups or chromatography, and provides the requisite polyamines in moderate to good yields. Graphical abstract image
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Ring-opening reaction of aziridines with amines under the influence of dimethyl sulfoxide ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Toshihiro Isobe, Takeshi Oriyama The ring-opening reaction of various aziridines with amines proceeded at room temperature to afford the corresponding 1,2-diamines in good to excellent yields using only 3–5equiv dimethyl sulfoxide (DMSO) to aziridines in hexane. This reaction can be performed with easy handling and proceeds under mild reaction conditions. Also a variety of amines are available as a nucleophile. Graphical abstract image
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An intramolecular cycloaddition of nitrones with tethered olefins: a versatile synthesis of hexahydro-3H-xantheno[1,2-c]isoxazoles ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Y. Jayaprakash Rao, E. Pravardhan Reddy, B. Sridhar, J.K. Lakshmi, B.V. Subba Reddy A variety of isoxazolidine and isoxazoline derivatives have been prepared through a 1,3-dipolar cycloaddition of alkene-tethered chromene-3-carbaldehydes with hydroxyl amines. This is the first example of the preparation of highly diastereoselective isoxazolidine derivatives from alkene appended chromene-3-carboxaldehyde. This method is operationally simple and works with a diverse range of substrates. Graphical abstract image
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Organocatalytic asymmetric synthesis of trans-configured trispirooxindoles through a cascade Michael-cyclization reaction ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Chaoling Wu, Linhai Jing, Dabin Qin, Mingxing Yin, Qiuzuo He An efficient stereoselective Michael-cyclization reaction of 3-isothiocyanato oxindoles to cyclic methyleneindolinones has been described. The protocol provides a facile and efficient access to chiral trans-configured trispirooxindoles containing two quaternary stereocenters in good yields (up to 89%) with good diastereoselectivities (up to 90:10) and high enantioselectivities (up to 94% ee) under mild conditions. Graphical abstract image
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Asymmetric alkylation or silylation of (S)-(−)-diphenylprolinol-derived α-silyl amide to synthesize optically pure α-monosilyl or bis(silyl) amides ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Zhenggang Huang, Lu Gao, Zhenlei Song Asymmetric alkylation or silylation of (S)-(−)-diphenylprolinol-derived α-silyl amide has been developed to synthesize optically pure α-monosilyl or bis(silyl) amides in good yields with high diastereoselectivity. Graphical abstract image
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Total synthesis of the tetracyclic indole alkaloid ht-13-A ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Yilin Zhang, Ian W. McArdle, Jeremiah W. Hubbard, Novruz G. Akhmedov, Björn C.G. Söderberg Total synthesis of the tetracyclic indole alkaloid ht-13-A is reported starting ultimately from commercially available (−)-4-amino-2-hydroxybutyric acid. The key steps in this synthesis are a Lewis acid mediated acyliminium ion allylation, a Mitsunobu reaction, a palladium catalyzed Stille-Kelly intramolecular cross coupling, and a carbon monoxide mediated palladium catalyzed reductive N-heterocyclization. Graphical abstract image
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DBSA-catalyzed Friedel–Crafts alkylation of cyclic ketene dithioacetals with alcohols in water ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Haifeng Yu, Peiqiu Liao A novel DBSA-catalyzed Friedel–Crafts alkylation of cyclic ketene dithioacetals, internal alkenes with highly nucleophilic carbon atom adjacent to the electron-withdrawing group, with alcohols in water has been developed. The reaction is efficient in the presence of catalyst loading as low as 10mol% in water at reflux, and a wide range of alkylated ketene dithioacetals are synthesized in excellent yields. Graphical abstract image
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Oxidative esterification of primary alcohols with TEMPO/CaCl2/Oxone under hydrous conditions ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Sven Hackbusch, Andreas H. Franz Symmetric esters are important compounds in the chemical industry, which creates demand for simple and efficient synthetic routes. Oxidative esterification is a promising method to achieve these aims. Here, we show that TEMPO/CaCl2/Oxone forms a convenient catalytic system for the synthesis of the aforementioned symmetric esters from primary alcohols in a biphasic dichloromethane–water solvent mixture. The substrate scope of the reaction method is complementary to those previously published and the terminal oxidant appears to play an important role. In addition, the method is shown to oxidize thiols preferentially over alcohol functional groups to give disulfide-bridged compounds. Graphical abstract image
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Total synthesis of (±)-Lingzhilactone B via semipinacol rearrangement ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Dong Chen, Xiao-Mei Li, Hao-Miao Liu, Ming-Ming Li, Yong-Xian Cheng, Hong-Bo Qin Total synthesis of (±)-Lingzhilactone B has been achieved for the first time in 13 steps. The key step features a semipinacol rearrangement to construct 5/5 bicyclic ring with adjacent quaternary carbon. Graphical abstract image
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Copper-catalyzed intramolecular oxidative amination of enaminone C–H bond for the synthesis of imidazo[1,2-a]pyridines ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Jie-Ping Wan, Deqing Hu, Ying Liu, Luyao Li, Chengping Wen The intramolecular C–N bond forming cross coupling reactions on the enaminones has been achieved for the synthesis of imidazole[1,2-a]pyridines via copper-catalyzed C(sp2)–H amination. This protocol provides a new route for the synthesis of 2-unsubstituted imidazole[1,2-a]pyridines via easily available starting materials. Graphical abstract image
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An enantioselective synthesis of the C3–C21 segment of the macrolide immunosuppressive agent FR252921 ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Arun K. Ghosh, Samuel Rodriguez An enantioselective synthesis of the C3–C21 segment of the novel immunosuppressant FR252921 is described. The C12 and C13 stereogenic centers were constructed by a non-aldol process utilizing optically active 4-phenylbutyrolactone. The C18 stereogenic center was installed using Braun’s highly diastereoselective acetate aldol reaction. Other key steps involved Curtius rearrangement and Horner–Wadsworth–Emmons olefination reactions. Graphical abstract image
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Microwave-assisted synthesis of functionalized spirohydantoins as 3-D privileged fragments for scouting the chemical space ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Hugues Prevet, Marion Flipo, Pascal Roussel, Benoit Deprez, Nicolas Willand Fragment-based drug design has been successfully applied to a large set of proteins, however in order to expand this concept to the most demanding targets, such as protein–protein interactions, it is required to enrich current fragment libraries with new and original 3D privileged fragments. Our goal was to develop a rapid microwave-assisted synthesis of 27 new privileged spirohydantoin fragments. Among them 24 compounds showed a high water solubility. These molecules were plotted according to the normalized principal moments of inertia of their minimized conformers, and most of the compounds were prone to occupy under-populated regions of the triangular plot. Finally we demonstrated that the hydantoin ring can be selectively N-monoalkylated providing the access to rapid functionalization for further elaboration. Graphical abstract image
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Stereoselective synthesis of a novel branched-chain (1S,2R,6R,7S)-7a-(hydroxymethyl)-1,2,6,7-tetrahydroxypyrrolizidine ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Jozef Gonda, Ján Elečko, Miroslava Martinková, Martin Fábian An efficient and highly stereoselective approach towards a new type of branched-chain pentahydroxylated pyrrolizidine 7 from a d-glucose isothiocyanate scaffold has been developed. The key features of this strategy are the construction of a diene-substrate foldamer possessing an amino functional group followed by subsequent ring-closing metathesis, an intramolecular cyclisation readily induced by regioselective tosylation to establish the pyrrolizidine unit and a highly diastereoselective, substrate-controlled dihydroxylation. Graphical abstract image
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A convenient and mild method for 1,2,4-oxadiazole preparation: cyclodehydration of O-acylamidoximes in the superbase system MOH/DMSO ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Sergey Baykov, Tatyana Sharonova, Angelina Osipyan, Sergey Rozhkov, Anton Shetnev, Alexey Smirnov Herein, we reported a general, convenient, and efficient synthesis of 3,5-disubstituted-1,2,4-oxadiazoles via cyclodehydration of O-acylamidoximes in the superbase system MOH/DMSO (M=Li, Na, K). Excellent isolated yields (up to 98%) were attained within short reaction times (10–20min). In addition, mild reaction conditions and a simple work-up procedure allow the synthesis of a wide range of heat-labile 1,2,4-oxadiazole-containing substances. Graphical abstract image
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Catalytic asymmetric synthesis of CPZEN-45 ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Toshifumi Takeuchi, Hikaru Abe, Takumi Watanabe, Masakatsu Shibasaki A catalytic asymmetric total synthesis of CPZEN-45 (1), anti-XDR-TB agent, was accomplished using a direct aldol reaction of a glycine Schiff base (3) and uridine-derived aldehyde (4) catalyzed by Zn(II)–(R,R)-linked-BINOL complex to give the desired stereoisomer selectively. The diazepinone ring system, another key structural element, was successfully constructed by vinyl halide–amide coupling promoted by Cu(I) salt. Graphical abstract image
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Rh(III)-catalyzed double molecular alkyne imine C–H activation: a facile and efficient synthesis of functionalized acridine compounds ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Yingying Shan, Weidong Yan The construction of a new nitrogen heterocyclic ring via the C–H activation is a facile and efficient protocol to afford polysubstituted acridine compounds from simple, readily available starting materials. In this Letter, functionalized benzo[c]acridine and thieno[3,2-c]acridine compounds have been accomplished by the method of Rh(III)-catalyzed double molecular alkyne imine C–H activation. Graphical abstract image
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A novel and resumable Schiff-base fluorescent chemosensor for Zn(II) ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Jun Yan, Long Fan, Jing-can Qin, Chao-rui Li, Zheng-yin Yang A new resumable Schiff-base fluorescent probe 7-methoxychromone-3-carbaldehyde-(3′-hydroxy-2′-naphthaleneformyl) hydrazone (L) was designed and synthesized for selective recognition Zn2+. With the titration and the ESI-MS spectra data, we reached the conclusion that the binding ratio between L and Zn2+ was determined to be 1. The sensor showed a strong fluorescence enhancement in ethanol system of Zn2+ (excitation 430nm and emission 498nm). And the enhancement may be due to CN isomerization and Photoinduced Electron Transfer (PET). Graphical abstract image
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Chemo-, regio-, and stereoselective hydroboration of conjugated enyne alcohol/amine: facile synthesis of Z,Z-/Z,E-1,3-dien-1/2-ylboronic ester bearing hydroxyl/amino group ()
Publication date: 29 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 26 Author(s): Hua-Dong Xu, Hao Wu, Chun Jiang, Peng Chen, Mei-Hua Shen Hydroboration of conjugated enyne alcohol/amine is studied by using copper salts and bis(pinacolato)diboron as pre-catalysts and boron source respectively. It is suggested that the chemo-selectivity is derived from a combined electronic influence of the heteroatoms on the substrate and the ligand on the transition metal. The regioselectivity is probably dominated mainly by electronic effect of the alkyne substituent. This study resulted in a highly selective protocol to access Z,Z-/Z,E-1,3-dien-1/2-ylboronic ester bearing hydroxyl/amino group. Graphical abstract image
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