Tetrahedron Letters

Editorial board ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24
>> read more

The impact of asymmetric organocatalysis in dearomatization and aromatization of carbocycles: increasing molecular complexity and diversity ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Loïc Pantaine, Xavier Moreau, Vincent Coeffard, Christine Greck The combination of asymmetric organocatalysis with either making or breaking aromaticity, in a single vessel, has known a rapid development over the last decade. This is due to its success in producing complex molecular architectures efficiently while maintaining a good control over diastereo- and enantioselectivities. This digest will offer a broad summary of the advances in this field, focusing primarily on carbocycles, and will be divided into two main parts: the first will concern combining asymmetric organocatalysis with dearomatization, the second with rearomatization. Graphical abstract image
>> read more

Multigram synthesis of an advanced nitroalkene intermediate: application in synthesis of octahydroindol-2-one derivative featuring diastereoselective Michael addition of diethylmalonate ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Shashikant B. Bhorkade, Kishor B. Gavhane Gram scale synthesis of a novel nitrocyclohexenetriol derivative is reported by applying intramolecular Henry reaction as a key step. Searching the utility of this scaffold, synthesis of hydroxylated octahydroindol-2-one derivative, which is a backbone of many amaryllidaceae alkaloids was also achieved via a very diastereoselective Michael addition of diethylmalonate to hydroxylated nitrocyclohexenetriol. Graphical abstract image
>> read more

Synthesis of multivalent difluorinated zanamivir analogs as potent antiviral inhibitors ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Zhao-Liang Yang, Xiong-Fei Zeng, Hai-Peng Liu, Qun Yu, Xin Meng, Zhong-Li Yan, Zhen-Chuan Fan, Hai-Xia Xiao, Suri S. Iyer, Yang Yang, Peng Yu An efficient synthesis of mono-, di-, tetra-, and octa-valent difluorinated zanamivir analogs as potent inhibitors of influenza virus is reported. The mono difluorinated zanamivir with an azide linker attached at the C-7 position was synthesized in good yield from sialic acid using Selectfluor® and (diethylaminosulfur trifluoride) DAST as the fluorination reagent. This key intermediate was attached on various alkynlated scaffolds via “Click Chemistry” to afford multivalent glycoclusters. A neuraminidase inhibition assay was used to evaluate the compounds for their inhibitory activity using H7N9 virus like particle. These multivalent sialosides show enhanced inhibition with IC50 values ∼100-fold better than the monomer indicative of the strength of using a multivalent approach. Graphical abstract image
>> read more

Synthesis under moderate pressure of 3-imidazo[1,2-a]pyridinylidene pyrrol-2-ones ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Nicolas Masurier, Aurélien Lebrun, Damien Canitrot, Jean-Michel Chezal, Emmanuel Moreau Conversion of 3-imidazo[1,2-a]pyridinylidene furan-2-ones into their pyrrol-2-one analogues was achieved efficiently with high yields, using a solution of ammonium hydroxide under moderate pressure conditions. A NMR study showed that the compounds are mainly isolated as E isomers. Graphical abstract image
>> read more

Chemoselective Cu(I) catalyzed bis(pinacolato)diboron conjugate addition and reduction onto α,β-unsaturated carbonyl compounds ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Qing-Dong Wang, Jin-Ming Yang, Dong Fang, Jiangmeng Ren, Bin Dong, Bin Zhou, Bu-Bing Zeng Ligand-free CuI-catalyzed bis(pinacolato)diboron (B2(pin)2) conjugate addition and reduction onto α,β-unsaturated carbonyl compounds in moderate to excellent yields has been demonstrated. Graphical abstract image
>> read more

Synthesis and anticancer evaluation of novel 9α-substituted-13-(1,2,3-triazolo)-parthenolides ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Mohamed Zaki, Hassan Allouchi, Abderrahman El Bouakher, Eric Duverger, Ahmed El Hakmaoui, Richard Daniellou, Gérald Guillaumet, Mohamed Akssira A series of novel 9α-substituted-13-(1,2,3-triazolo)-parthenolides 3–20 were efficiently synthesized and tested for their in vitro anticancer activity using the MTT colorimetric assay against four human cancer cell lines. 9α-Substituted-13-(1,2,3-triazolo)-parthenolide derivatives were prepared by the diastereoselective Michael addition of TMSN3 onto 9α-hydroxyparthenolide 1 to give the key intermediate 9α-trimethylsilyloxy-13-(1,2,3-triazolo)-parthenolide 2 which was utilized in a regioselective Huisgen 1,3-dipolar cycloaddition reaction with various alkynes to afford 1,4-disubstituted-1,2,3-triazoles of 9α-substituted-parthenolide. Graphical abstract image
>> read more

Synthesis of lactosamine from lactulose: scalable approach for the Heyns rearrangement ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Károly Ágoston, Gyula Dékány, István Bajza, Markus Hederos A scalable approach for the preparation of lactosamine hydrochloride from lactulose is described. The reported procedure is based on the preparation of a new dibenzylamino derivative of lactosamine hydrochloride. Lactosamine hydrochloride was prepared in a two-pot reaction sequence from commercially available lactulose. Graphical abstract image
>> read more

Acid catalyzed condensation of levulinic acid with glyoxylic acid: synthesis of 1-methyl-2,8-dioxabicyclo[3.3.0]oct-4-ene-3,7-dione ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Ananda S. Amarasekara, Uyen Ha The sulfuric acid catalyzed condensation of levulinic acid with glyoxylic acid at 80°C, for 24h under neat conditions gives 1-methyl-2,8-dioxabicyclo[3.3.0]oct-4-ene-3,7-dione in 92% yield. Catalytic reduction of this unsaturated bis-lactone provides a facile route to produce polyester monomer 1-methyl-2,8-dioxabicyclo[3.3.0]octane-3,7-dione from renewable feedstocks. Graphical abstract image
>> read more

A convergent preparation of the CHK1 inhibitor MK-8776 (SCH 900776) ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Marc A. Labroli, Michael P. Dwyer, Cory Poker, Kerry M. Keertikar, Randall Rossman, Timothy J. Guzi This Letter describes the development of a convergent, efficient route to the CHK1 inhibitor MK-8776. This synthetic approach relies upon the cyclization of a bispyrazole adduct 10 with a optically pure β-keto nitrile 9 to construct the pyrazolo[1,5-a]pyrimidine scaffold in a single step. Graphical abstract image
>> read more

Diketopiperazines derivatives isolated from Bacillus thuringiensis and Bacillus endophyticus, establishment of their configuration by X-ray and their synthesis ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Estibaliz Sansinenea, Francisco Salazar, Jacqueline Jiménez, Ángel Mendoza, Aurelio Ortiz Four known diketopiperazines have been isolated from Bacillus thuringiensis strain and two of them were isolated from Bacillus endophyticus also. Their structure was elucidated by a complete spectroscopy and the configuration of three of them was established by X-ray analysis. The dicetopiperazine cyclo-(l-Proline-l-Tyrosine), isolated from both strains, was polymorphic showing different physical properties. The synthesis has been successfully realized in two simple steps. Their biological activities were probed against some Gram-positive and Gram-negative bacteria and six fungi. The results indicated that these compounds had no antibacterial activity but they had antifungal activity. Graphical abstract image
>> read more

Single precursor for the synthesis of donor and acceptor units of the low band gap polymers: synthesis of benzodithiophene and thienopyrroledione from maleic anhydride ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Vinay S. Kadam, Arun L. Patel, Sanjio S. Zade An efficient route was developed to synthesize dimethyl thiophene-3,4-dicarboxylate from maleic anhydride. Dimethyl thiophene-3,4-dicarboxylate was used as a single precursor for synthesis of benzo[1,2-b:4,5-b′]dithiophene (BDT) and Thieno[3,4-c]pyrrole-4,6-dione (TPD) derivatives. BDT and TPD derivatives have been highly exploited as donor and acceptor units, respectively, to synthesize important donor–acceptor (D–A) conjugated polymers. BDT-based polymers were found to be one of the most efficient conjugated polymers for organic photovoltaic application. Synthesis of quinone precursor of the dihydroxybenzothiophene was accomplished by a new and unconventional methodology which includes reaction of 3,4-thiophene dicarboxylate with sodium hydride in THF. Dithienobenzoquinone dicarboxylate and dihydroxybenzodithiophene dicarboxylate were characterized structurally by single-crystal X-ray diffraction. Both compounds show strong π-stacking interaction and arrange in the parallel molecular sheets in the crystals. Graphical abstract image
>> read more

Transition metal-free steric controlled one-pot synthesis of highly substituted N-amino 1,2,3-triazole derivatives via diazo transfer reaction from β-keto esters ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Rajendran Nagarajan, Jayadevan Jayashankaran, Lourdusamy Emmanuvel An efficient, simple protocol for the one-pot synthesis of N-amino 1,2,3-triazole from β-keto esters has been described. This method involves diazo transfer reaction into in situ generated hydrazones using imidazole sulfonyl azide as the nitrogen source. This protocol does not involve any transition metal and can be regarded as a general method for the synthesis of N-amino 1,2,3-triazole from hydrazones. Graphical abstract image
>> read more

A new Rhodamine-based visual and fluorometric probe for selective detection of trivalent cations ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Shuhua Hou, Zhongguo Qu, Keli Zhong, Yanjiang Bian, Lijun Tang A novel Rhodamine-based probe L has been designed and synthesized. Probe L acted as a colorimetric and fluorescent ‘turn on’ probe for trivalent ions with high selectivity over other monovalent or divalent ions in CH3OH/Tris (8:2). Furthermore, probe L exhibited low detection limits toward these trivalent ions (Fe3+, Al3+ and Cr3+) which could make it attractive in trivalent ion detection. Graphical abstract image
>> read more

Direct synthesis of nitriles from cleavage of CC double bond with nitrite as the nitrogen source and oxidant ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Qiang Liu, Bao Fang, Xiaohui Bai, Yuan Liu, Yao Wu, Guiming Xu, Cancheng Guo The transformation of the CC bond of olefin to nitriles has been developed, using easily available NaNO2 as both the nitrogen source and oxidant. Several aryl, heterocyclic nitriles with various substituting groups could be successfully prepared in good to high yields. Based upon experimental observations, a possible reaction mechanism is proposed. Graphical abstract image
>> read more

Photoinduced double perfluoroalkylation of methylacenes ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Emiko Nogami, Yuri Washimi, Takashi Yamazaki, Toshio Kubota, Tomoko Yajima Novel photoinduced double perfluoroalkylation of methylacenes has been described. The reaction proceeded with appropriately substituted methylacenes to produce a mixture of the expected aromatic compounds with Rf groups both at the methyl and its para position as well as the corresponding nonaromatic tautomers. Steric repulsive interaction of fluorine atoms in perfluoroalkyl groups with hydrogen atoms at the peri positions would be the most significant factor for control of ratios of these products. Graphical abstract image
>> read more

Studies directed toward synthesis of taepeenin D: construction of the C4 stereogenic center and the CD benzofuran rings ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Yuichiro Nakazawa, Meri Nagatomo, Tsuyoshi Oikawa, Masato Oikawa, Yuichi Ishikawa Taepeenin D is a meroterpenoid isolated from roots and stems of Caesalpinia crista, showing inhibitory activity of Hedgehog signaling pathway. Herein we report selective and short-step construction of two fragments of taepeenin D. First, we demonstrated alkoxy radical-mediated selective functionalization at C19 methyl group for construction of the C4 quaternary carbon stereogenic center. Second, the CD benzofuran rings were constructed in 6 short steps from decalone. The synthesis described herein is not only applicable to total synthesis, but also used for study of the structure–activity relationships of taepeenin D. Graphical abstract image
>> read more

First total synthesis of 6-epi-phomonol ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Fátima Garrido, Hugo Santalla, Generosa Gómez, Yagamare Fall We describe a new and efficient total synthesis of 6-epi-phomonol from commercially available tri-O-acetyl-d-glucal. A key feature of the synthesis involves a stereoselective Michael addition using a magnesium cyanocuprate. Graphical abstract image
>> read more

A facile and expeditious approach to substituted 1H-pyrazoles catalyzed by iodine ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Hailei Zhang, Qian Wei, Guodong Zhu, Jingping Qu, Baomin Wang A facile and expeditious method for the synthesis of 1H-pyrazoles by the reaction of α,β-unsaturated aldehydes/ketones and sulfonyl hydrazide catalyzed by as low as 2mol% I2 has been demonstrated. This synthetic system features simple operation and mild reaction conditions, and displays a broad functional group tolerance furnishing good to excellent yields. Graphical abstract image
>> read more

An environmentally benign approach for the synthesis of 3,4,5-trisubstituted 2-aminofurans under solvent-free conditions via isocyanide-based multicomponent approach ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Tariq A. Shah, Zubair Ahmad, N.P. Rath, M. Muneer An efficient solvent-free procedure for the synthesis of 3,4,5-trisubstituted 2-aminofurans has been developed via a multicomponent strategy by the solid state condensation of finely grounded dibenzoylacetylene and aromatic aldehydes in the presence of isocyanides at room temperature. Clean reaction profile, easy work-up procedure, non-chromatographic purification technique, short reaction times, high yields, and solvent-free reaction conditions are the remarkable advantages of this procedure. Single crystal X-ray diffraction has been established for four structures. Graphical abstract image
>> read more

Catalyst-free direct difunctionalization of alkenes with H-phosphine oxides and dioxygen: a facile and green approach to β-hydroxyphosphine oxides ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Meng-Shun Li, Qiang Zhang, Dong-Yan Hu, Wen-Wu Zhong, Ming Cheng, Jian-Xin Ji, Wei Wei A simple and catalyst-free method has been developed for the construction of β-hydroxyphosphine oxides through direct difunctionalization of alkenes with H-phosphine oxides and dioxygen under mild conditions. Preliminary mechanistic studies indicated that the hydroxyl oxygen atom of β-hydroxyphosphine oxide originated from the dioxygen and the present reaction might involve a radical process. Graphical abstract image
>> read more

Photochromism of boron difluoride-based diarylethenes ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Yaqian Li, Qifei Lin, Qian Li, Sa Wang, Ronghua Tan, Shuzhang Xiao The synthesis and characterization of two novel photochromic diarylethenes containing boron difluoride chromophores is described. The boron difluoride chromophores are connected directly to the thiophene rings and participate in the photoisomerization reaction. X-ray single crystal structure analysis of the diarylethenes indicates that intermolecular planar π–π interactions are significantly alleviated, due to various intermolecular non-covalent bondings. Therefore, they show almost the same fluorescent properties in the solid state as in dilute chloroform solutions. These two diarylethenes show typical photochromic properties in chloroform and also in poly(methyl methacrylate) film. During the photochromism, fluorescence of the diarylethenes could be reversibly tuned. Graphical abstract image
>> read more

Synthesis of tyrosyl-DNA phosphodiesterase I inhibitors ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Sagar D. Nale, Vrushali H. Jadhav The first report for the synthesis of tyrosyl-DNA phosphodiesterase I inhibitors 3,4-dimethoxyphenol-1-β-d-(6′-O-galloyl)glucopyranoside 3 and 3-(4-hydroxy-3-methoxyphenyl)propane-1,2-diol 2-β-d-(6′-O-galloyl) glucopyranoside 5 has been accomplished starting from readily available d-glucose as a starting material. An efficient and general approach has been reported for the synthesis of compounds 3 and 5 with an overall yield of 26% and 27%, respectively. Graphical abstract image
>> read more

Detection of Hg2+ by a FRET ratiometric fluorescent probe based on a novel BODIPY-RhB system ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Dandan Cheng, Wenqi Zhao, Hongzhi Yang, Ziping Huang, Xingliang Liu, Aixia Han A novel BODIPY-RhB ratiometric fluorescent probe 1 for Hg2+ based on a fluorescence resonance energy transfer mechanism has been developed. In this system, the energy transfer efficiency is 94.8%. The BODIPY-RhB probe 1 can detect Hg2+ ions with a very low detection limit of 1.56ppb, and very high selectivity toward Hg2+ ions. Graphical abstract image
>> read more

A mild and selective protecting and reversed modification of thiols ()
Publication date: 15 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 24 Author(s): Xiangmin Li, Hongxian Li, Wei Yang, Jinchen Zhuang, Hao Li, Wei Wang One selective thiol-protecting study has been investigated for a wide range of thiols including general thiols and thiols containing multiple functional groups. The reactions of bromomaleimides and thiols under the mild condition afforded the protected products in excellent yields. The thiols can be recovered very quickly using dithiothreitol (DTT) under the mild condition. Graphical abstract image
>> read more

Editorial board ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23
>> read more

Practical way for the synthesis of phosphine oxides and phosphine sulfides from benzyl alcohol derivatives ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Yutao Ma, Feng Chen, Jifeng Bao, Hao Wei, Min Shi, Feijun Wang The reaction of benzyl alcohol derivatives with Ph2PI generated in situ from Ph2PCl and NaI provides a facile way to the synthesis of pentavalent phosphine compounds with moderate to excellent yields. Graphical abstract image
>> read more

Pamam built-on-silicon wafer thin-layer extraction devices for selective metal contamination detection ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Oscar Valdés, Claudia Vergara, Fabiane M. Nachtigall, Zoraya Lopez-Cabaña, Jaime Tapia, Leonardo S. Santos Silicon wafer surface was modified with polyamidoamine (PAMAM G0) dendrimer and further characterized by AFM, MALDI-MS, SEM, and EDX to provide a new sensor for metallic ions. The characterization showed the effective immobilization of dendrimer on the surface, and the analysis performed by MALDI-MS also showed a characteristic signal for each dendrimer–metal complex, which confirms the presence of the metal in solutions. The proof-of-concept of this device was tested as sensor for metal ions such as Cu(II) and U(VI) and using calibration curves the amount of metallic ions dissolved in solution can be easily assessed. The PAMAM G0 supported in silicon wafer can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction device for metal determination with ‘on-spot’ MALDI-TOF-MS detection. Graphical abstract image
>> read more

Conversion of β-glycopyranoside to α-glycopyranoside by photo-activated radical reaction ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Yu-Chen Lai, Chin-Hung Luo, Hsin-Chun Chou, Cheng-Jhang Yang, Le Lu, Chien-Sheng Chen By using carbon tetrachloride as the chloride radical and boron trifluoride etherate as the Lewis acid, the halogen-light-activated anomeric inversion of glycoside was achieved. This reaction is a novel guide to invert the glycosidic bond from a β-anomer to an α-anomer. Graphical abstract image
>> read more

A fluorescein-based fluorescence probe for the fast detection of thiol ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Yunchang Liu, Kaiqiang Xiang, Baozhu Tian, Jinlong Zhang A new turn-on fluorescent probe for the selective detection of thiol over other amino acids was synthesized. Probe possesses the widely-used thiol-selective 2,4-dinitrobenzenesulfonyl (DNBS) group which can react with thiol and release the fluorescein which has strong fluorescence. Fluorescein, a well known xanthene fluorescent dye, has two states at different environment. Fluorescein is in the state of spirocyclization when connected with 2,4-dinitrobenzenesulfonyl (DNBS) group which has no fluorescence. However, it is in the state of open form when it reacts with thiol which has a strong fluorescence. The transition of the two states can be used to selectively detect thiol and the color can change from colorless to yellow which can be differentiated by naked eyes. Upon the titration of thiol, the absorption band at 454nm rises gradually and the fluorescence emerges at 521nm and the detection limit can be as low as 0.16μM. All of such good properties prove it to be a good sensor for the selective detection of thiol and it shows a potential use in bioimaging applications. Graphical abstract image
>> read more

Novel chemoenzymatic synthesis of an enantiopure allo-inosamine hexaacetate from benzyl azide ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Victoria de la Sovera, Pablo Garay, Natalia Thevenet, Mario A. Macías, David González, Gustavo Seoane, Ignacio Carrera A facile and short chemoenzymatic synthesis of (−) 1L-5-amino-5-deoxy-allo-inositol hexaacetate is described using benzyl azide as starting material. The key transformations consist of an enzymatic dioxygenation using the toluene dioxygenase enzymatic complex, followed by an allylic azide double sigmatropic [3,3] shift to introduce the nitrogen functionality in the ring in a stereoselective manner. Azide reduction and further regioselective oxidation of the diene moiety afforded the desired inosamine in only eight steps from benzyl azide. Graphical abstract image
>> read more

Palladium-catalyzed double C–H functionalization of 2-aryl-1,3-dicarbonyl compounds: a facile access to alkenylated benzopyrans ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Subrahmanyam Choppakatla, Aravind Kumar Dachepally, Hari Babu Bollikolla The present study reports the development of a palladium-catalyzed oxidative annulation/nucleophilic substitution sequence affording a library of alkenylated benzopyrans using 2-aryl-1,3-dicarbonyl compounds and allylic acetate. The process is compatible to a wide range of substrates with good functional group tolerance producing the desired heterocycles in moderate to good yields. Graphical abstract image
>> read more

Enantioselective borane reduction of ketones catalyzed by tricyclic 1,3,2-oxazaborolidines ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Johannes Kaldun, Alexander Krimalowski, Matthias Breuning Two novel tricyclic 1,3,2-oxazaborolidines were synthesized in seven steps from methyl Boc-l-pyroglutamate. They are characterized by an ortho- and peri-fused 5/5/6-ring system with the B–N bond forming one ring junction. In the asymmetric borane reduction of ketones, the B-alkoxy bridged derivative permits excellent enantioselectivities of up to 98% ee and its activity is comparable to that of the standard CBS catalyst. The closely related, B-alkyl bridged derivative is less enantioselective and less active, as determined by competition experiments. Graphical abstract image
>> read more

Synthesis and antioxidant properties of novel 2H-chromene-3-carboxylate and 3-acetyl-2H-chromene derivatives ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Paramasivam Sivaguru, Raman Sandhiya, Mani Adhiyaman, Appaswami Lalitha In this communication, for the first time we have constructed a series of novel azo group fused 2H-chromene-3-carboxylate and 3-acetyl-2H-chromene derivatives via the Knoevenagel condensation reaction of active methylene compounds with aromatic 5-arylazosalicylaldehydes followed by a nucleophilic addition of the phenolic hydroxyl group to the carbonyl group of one of the ester groups. Shorter reaction times, high yields, simple work-up procedure and mild reaction conditions are the advantages of the present method. In addition, we have also studied the antioxidant activities using DPPH, hydroxyl, and ABTS radical scavenging methods. Graphical abstract image
>> read more

Visible light induced azidation of aldehydic C–H with carbon tetrabromide and sodium azide ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Vinod K. Yadav, Vishnu P. Srivastava, Lal Dhar S. Yadav A convenient and highly efficient synthesis of acyl azides via visible light induced azidation of aldehydic C–H with carbon tetrabromide and sodium azide is reported. The approach is also, applicable to a one-pot synthesis of carbamoyl azides starting directly from aldehydes. Operational simplicity, good to excellent yields and utilization of visible light as an inexpensive and sustainable energy source are the salient features of the present protocol. Graphical abstract image
>> read more

A chemoselective ipso-hydroxylation of arylboronic acids using urea-hydrogen peroxide under catalyst free condition ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Surabhi Gupta, Priyanka Chaudhary, Vandana Srivastava, Jeyakumar Kandasamy An efficient and practical method for the chemoselective ipso-hydroxylation of arylboronic acids is demonstrated using urea-hydrogen peroxide under catalyst free condition at room temperature. Remarkably, oxidation sensitive functional groups such as olefin, aldehyde, alcohol, ketone, and sulfide as well as heterocycles such as pyridine and thiophene were tolerated under the standard reaction condition. In addition to the solution phase, a solid phase ipso-hydroxylation of arylboronic acids has been investigated with urea hydrogen peroxide. The scope and limitations of the solid phase protocol is discussed. Graphical abstract image
>> read more

Palladium-catalyzed ortho-acylation of N-Nitrosoanilines with α-oxocarboxylic acids: a convenient method to synthesize N-Nitroso ketones and indazoles ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Liang Zhang, Zhe Wang, Peiyu Guo, Wei Sun, Ya-Min Li, Meng Sun, Chengwen Hua An efficient and mild protocol for regioselective synthesis of N-Nitroso aryl ketones by palladium-catalyzed direct acylation of arenes using N-Nitroso as directing groups is described. This reaction proceeded smoothly and could tolerate a variety of functional groups. Moreover, this chemistry offers a convenient access to a range of indazoles. Graphical abstract image
>> read more

Iodine-catalyzed synthesis of 5H-phthalazino[1,2-b]quinazoline and isoindolo[2,1-a]quinazoline derivatives via a chemoselective reaction of 2-aminobenzohydrazide and 2-formylbenzoic acid in ionic liquids ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Rong-Zhang Jin, Wen-Ting Zhang, Yu-Jing Zhou, Xiang-Shan Wang A chemoselective reaction of 2-aminobenzohydrazides and 2-formylbenzoic acid is described for the synthesis of 5H-phthalazino[1,2-b]quinazoline and isoindolo[2,1-a]quinazoline derivatives in ionic liquids catalyzed by iodine. It is found that the type of the products depends on the steric effect in the reactant of 2-aminobenzohydrazides. Graphical abstract image
>> read more

A new general method for the synthesis of thiophenes through acid mediated cyclization of mixed acetals derived from β-oxodithiates and bromoacetaldehyde acetal ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): C.S. Pradeepa Kumara, G. Byre Gowda, N. Ramesh, M.P. Sadashiva, H. Junjappa β-oxodithioates react with bromoacetaldehyde diethylacetal in the presence of anhydrous potassium carbonate in dimethyl formamide at 80°C to yield the corresponding mixed acetals. These acetals undergo smooth cyclization in the presence of ethanolic orthophosphoric acid to afford the corresponding 2-methylthio-3-acyl/aroyl/heteroaroyl thiophenes in 64–85% high overall yields. Graphical abstract image
>> read more

A depsidone and six triterpenoids from the bark of Garcinia celebica ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Thai Q. Bui, An T. Bui, Kien T. Nguyen, Vy T. Nguyen, Binh T.D. Trinh, Lien-Hoa D. Nguyen A new depsidone, garcinisidone H (1), and six novel triterpenoids, were isolated from the bark of Garcinia celebica. The latter compounds consisted of two lanostanes, (E)-3β,9α-dihydroxylanosta-24-en-26-oic acid (2) and 3,23-dioxo-9,16-lanostadien-26-oic acid (3), and four friedolanostanes, (24E)-3-oxo-17,14-friedolanosta-8,14,24-trien-26-oic acid (4), (22Z,24E)-9α-hydroxy-3-oxo-17,13-friedolanosta-12,22,24-trien-26-oic acid (5), (22Z,24E)-3-oxo-17,14-friedolanosta-8,14,22,24-tetraen-26-oic acid (6) and (22Z,24E)-9α-hydroxy-3-oxo-13α,30-cyclo-17,13-friedolanosta-22,24-dien-26-oic acid (7). In addition, twelve known compounds were obtained. The structures of the new compounds were elucidated using spectroscopic methods, mainly 1D and 2D NMR. The cytotoxicity of the isolated compounds against the human breast cancer cell line MCF-7 was evaluated using the sulforhodamine B assay, in which macluraxanthone exhibited the strongest activity with an IC50 of 6.1μM. Graphical abstract image
>> read more

Stepwise iododesilylation and coupling reaction: a flexible route to 2,4-disubstituted-1H-pyrroles ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Jianhui Liu, Nanyan Fu, Changyun Wei, Zhucao Song In this study, we report a new strategy for the synthesis of 2,4-disubstituted pyrroles using a stepwise iododesilylation and palladium-catalysed Suzuki coupling reaction of 2,4-bis(trimethylsilyl)-1-t-Boc-1H-pyrrole (2). The regioselective iodo-desilylation followed by the Suzuki coupling reaction with concomitant Boc deprotection are critical aspects of the new synthesis method. Graphical abstract image
>> read more

Enantioselective synthesis of spirocyclic tetrahydrothiophene derivatives bearing a benzofuran-3(2H)-one scaffold. Unusual supramolecular crystal structure with high Z′ ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Dorota Kowalczyk, Jakub Wojciechowski, Łukasz Albrecht Herein, we report our studies on the enantioselective synthesis of spirocyclic tetrahydrothiophene derivatives bearing a benzofuran-3(2H)-one scaffold. The developed method utilizes 2-arylidenebenzofuran-3(2H)-ones and 2-thioacetaldehyde, generated in situ from 1,4-dithiane-2,5-diol, as starting materials and proceeds in a cascade manner involving a thio-Michael-aldol reaction sequence. The absolute configuration of the obtained tetrahydrothiophenes was assigned by single crystal X-ray analysis. Unusually high Z′ crystal packing was found in the crystal. Graphical abstract image
>> read more

Azobenzene-bridged bile acid dimers: an interesting class of conjugates with conformation-controlled bioactivity ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Weina Li, Yan Li, Xianpeng Yin, Yun Liang, Jian Li, Chen Wang, Yue Lan, Hui Wang, Yong Ju, Guangtao Li The synergetic combination of the distinct properties of azobenzene and bile acid could afford stable tweezer-like conformation with tunable hydrophilic and hydrophobic channels, thus increasing their antimicrobial activity toward both Gram-positive and Gram-negative bacteria, which can be conveniently switched off when the conformation turn back to the extended state. Graphical abstract image
>> read more

Stimuli-response fluorescence behaviors of dimesitylboron functionalized with tetraphenylethylene ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Junhui Jia, Pengchong Xue, Ran Lu New dimesitylborylthiophene derivative with terminal tetraphenylethene TPETB has been synthesized. It was found that TPETB exhibited aggregation-induced emission behavior and reversible mechanofluorochromism. For instance, the emission intensity of TPETB in THF/H2O with water fraction of 90% was ca. 21 times higher than that in THF. In addition, grinding the as-prepared crystal of TPETB the emitting color changed from sky blue to yellowish green. Meanwhile, the ground powder could recover to crystalline structure with sky blue emission when it was exposed to CH2Cl2 vapor. It was suggested that the transformation between crystalline and amorphous states led to the changes of solid emitting colors in response to external mechanical forces. It should be noted that TPETB could detect F− selectively, and the detection limit was 1.67×10−8 mol/L in CH2Cl2. Graphical abstract image
>> read more

Synthesis of novel eight-membered dibenzo[b,f][1,5]oxazocin-6-ones ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Paramasivam Sivaguru, Kandasamy Parameswaran, Appaswami Lalitha Herein, we wish to report the scandium triflate catalyzed synthesis of novel dibenzo[b,f][1,5]oxazocin-6-ones in PEG-400 as a greener medium. Using this simple and greener protocol, for the very first time we have constructed novel eight-membered heterocyclic compounds in good yields. The PEG-Sc(OTf)3 catalytic system can be reused for four consecutive runs without any significant loss of its catalytic activity. Graphical abstract image
>> read more

Enantioselective synthesis of syn-2-amino-1,3-diols via organocatalytic sequential oxa-Michael/α-amination reactions of α,β-unsaturated aldehydes ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Jiang Weng, Lin-Jie Huang, Liang Long, Ling-Yi Xu, Gui Lu A general and efficient method for the enantioselective synthesis of syn-2-amino-1,3-diols is reported. It involves the methodology of secondary amine-catalyzed one-pot sequential oxa-Michael/α-amination reactions of α,β-unsaturated aldehydes. This method has also been successfully applied to highly efficient total syntheses of (+)-safingol and d -threo-clavaminol H with excellent stereoselectivities. Graphical abstract image
>> read more

Hydrogen bonding network-assisted chemiluminescent thermal decomposition of 3-hydroxyphenyl-substituted dioxetanes in crystal ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Nobuko Watanabe, Hikaru Takatsuka, Hisako K. Ijuin, Ayu Wakatsuki, Masakatsu Matsumoto Bicyclic dioxetane 1 bearing a 3-hydroxyphenyl group underwent thermal decomposition in solution (TD soln ) to form 3-oxopentyl 3-hydroxybenzoate 4 accompanied by the emission of light [λ max CL (TD soln )=405nm] due to an excited 3-oxopentyl group in 4. Dioxetane 1 also exclusively gave 4 by thermal decomposition in crystal (TD cryst ). However, in contrast to TD soln , TD cryst of 1 gave light [λ max CL (TD cryst )=464nm] due to excited oxidobenzoate 3 ∗ and/or its closely related species formed by CTID (charge-transfer induced decomposition) mechanism. The unique chemiluminescent TD cryst of 1 was presumably the result of hydrogen bonding formed in the crystal between the phenolic proton of a dioxetane molecule and a peroxide oxygen of another dioxetane molecule. In this work, TD cryst as well as TD soln of bicyclic dioxetane analog bearing a 4-fluorenyl-3-hydroxyphenyl moiety 10 and of adamantylidene-dioxetane bearing a 3-hydroxyphenyl group 5b were also investigated. Graphical abstract image
>> read more

2-(Phenylseleno)ethanesulfon-amide as a novel protecting group for aniline that can be deprotected by a radical reaction ()
Publication date: 8 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 23 Author(s): Nobuhiro Kihara, Yuji Mitsuhashi, Makoto Sato, Shun-ichi Hirose, Erika Goudo, Yoshinori Uzawa, Natsumi Shirai, Sari Hamamoto, Ryo Iwasaki, Akane Fujioka Anilines were protected as 2-(phenylseleno)ethanesulfonanilide (SeES anilide) via sulfonylation by 2-chlorosulfonyl chloride followed by the conjugate addition of benzeneselenol. The SeES anilide was deprotected by radical reduction using tributyltin hydride in the presence of AIBN. The corresponding anilines were obtained in high yields when the hydride and AIBN were added to the system slowly. Since the radical reaction proceeds under neutral conditions, chemoselective deprotection of the SeES group was accomplished. The SeES anilide was stable under various conditions, including some severe conditions. Graphical abstract image
>> read more

Editorial board ()
Publication date: 1 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 22
>> read more

Baker’s yeast as an efficient biocatalyst for regioselective 1,4-conjugate addition of indoles to nitroolefins in aqueous medium ()
Publication date: 1 June 2016 Source:Tetrahedron Letters, Volume 57, Issue 22 Author(s): Ananda Mane, Trushant Lohar, Rajashri Salunkhe The 1,4-conjugate addition of indoles to nitroolefins was efficiently carried out in aqueous media using baker’s yeast as a biocatalyst at room temperature. The merits of the present method are operational simplicity, easy workup, utilization of an inexpensive catalyst, free from hazardous organic solvents and good yields of products. The generality of this method was demonstrated by synthesizing an array of diverse 3-substituted indole derivatives and could be extended for dialkylation of 1,4-bis-(2-nitrovinyl)benzene. Graphical abstract image
>> read more

Site Search