Tetrahedron Letters

Editorial board ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9
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Microwave-assisted direct esterification of cyclic phosphinic acids in the presence of ionic liquids ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Nóra Zsuzsa Kiss, György Keglevich The efficiency of the microwave-assisted direct esterification of cyclic phosphinic acids was significantly enhanced by adding 10% of an ionic liquid to the reaction mixture prior to irradiation. In the presence of [bmim][PF6] most of the esterifications were complete within 30min at 180°C. Graphical abstract image
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Cu2+-selective ratiometric fluorescence signaling probe based on the hydrolysis of dansylhydrazine ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Myung Gil Choi, Jieun Kim, Ja Min Hong, In Jung Chang, Sangdoo Ahn, Suk-Kyu Chang A simple Cu2+-selective ratiometric fluorescence signaling probe based on the hydrolysis of dansylhydrazine was developed. Dansylhydrazine 1 showed prominent ratiometric fluorescence signaling behavior toward Cu2+ ions in a 50% aqueous (pH 7.4) acetonitrile solution. The ratiometric signaling behavior was due to the Cu2+-assisted hydrolysis of the yellow-colored fluorescent dansylhydrazine to strongly blue-fluorescent dansyl acid. The Cu2+-selective signaling of probe 1 was not affected by the presence of biologically important metal ions. The ratiometric signaling of Cu2+ by 1 was possible with a detection limit of 6.0×10−8 M (3.8ppb). In addition, the signaling of Cu2+ in biological samples using synthetic urine was also tested. Graphical abstract image
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Synthesis and photophysical properties of a new BODIPY-based siloxane dye ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Alexey A. Pakhomov, Yuriy N. Kononevich, Maria V. Stukalova, Evgeniya A. Svidchenko, Nikolay M. Surin, Georgy V. Cherkaev, Olga I. Shchegolikhina, Vladimir I. Martynov, Aziz M. Muzafarov A fluorescent dye comprising four BODIPY derivatives conjugated to a cyclotetrasiloxane core was synthesized by consecutive hydrosilylation and esterification reactions. Photophysical properties of the dye in various organic solvents were investigated. It was shown that due to a fourfold extinction coefficient increase and a moderate quantum yield decrease the brightness of the tetra-BODIPY dye in low-polarity solvents, calculated per molecule, increased 3 times when compared to mono-BODIPY. By contrast, in polar solvents there was a dramatic drop in brightness apparently associated with intramolecular interactions of the low-polar BODIPY chromophores. Graphical abstract image
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Dual oxidation/bromination of alkylbenzenes ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Marwa M. Aborways, Wesley J. Moran In the presence of sodium bromide and Oxone, a range of alkylbenzene derivatives are brominated and/or oxidized with up to four C-H bonds being functionalized. Graphical abstract image
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New catalytic route for the synthesis of an optically active tetralone-derived amine for rotigotine ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Christopher J. Cobley, George Evans, Tamara Fanjul, Shaun Simmonds, Amy Woods Rotigotine is a launched drug for the treatment of Parkinson’s disease and restless legs syndrome. The key steps of an alternative route for the synthesis of rotigotine have been demonstrated. Formation of a prochiral enamide, asymmetric hydrogenation of the enamide with high enantioselectivity, and reduction of the resulting amide to an amine have been proved to work successfully. The best conditions screened to date for the asymmetric hydrogenation of enamide 9 to amide 10 were with [(RuCl((R)-T-BINAP))2(μ-Cl)3][NH2Me2] at 25bar H2 and 30°C (500:1 S/C ratio, 99% conversion, 91% ee S). Reduction of amide 10 to amine 5 was best achieved with Red-Al giving 95% conversion. Graphical abstract image
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Facile synthesis of hexahydropyrazino[2,3-e]pyrazines from 3-aminomethyl-1,2,4-triazoles ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Dmytro M. Khomenko, Roman O. Doroschuk, Vladimir V. Trachevskii, Sergiu Shova, Rostyslav D. Lampeka The cyclocondensation of aminomethyl-1,2,4-triazoles and glyoxal gives hexahydropyrazino[2,3-e]pyrazines in good yields. 1H and 13C NMR spectra of the title compounds are described and the molecular structure of 4a,5,6,10a,11,12-hexahydro-(4aR,10aR)-[1,2,4]triazolo[1,5-a][1,2,4]triazolo[1′,5′:1,6]pyrazino[2,3-e]pyrazine was established by single crystal X-ray analysis. Graphical abstract image
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One-pot synthesis of 4-(phenylselanyl)-substituted pyrazoles ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Metin Zora, Deniz Demirci, Arif Kivrak, Yilmaz Kelgokmen A facile, one-pot, general synthetic method for the preparation of 4-(phenylselanyl)pyrazoles is described. When reacted with hydrazines, α,β-alkynic aldehydes produced in situ α,β-alkynic hydrazones, which, upon treatment with phenylselenyl chloride, undergo cyclization to afford 4-(phenylselanyl)pyrazoles in good to high yields. This cyclization has been found to be general for a variety of in situ generated α,β-alkynic hydrazones and exhibits good tolerance to a broad range of substituents, including electron-donating and electron-withdrawing groups. The enrichment of the pyrazole core with a selenyl moiety as well as with aryl and/or ferrocenyl groups may offer potential for the synthesis of molecules with pronounced or distinct biological activities. Graphical abstract image
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Synthesis and electronic properties of thiadiazole[3,4-c]pyridine copolymers for solar cell application ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Chinna Bathula, Pranav Kalode, Supriya Patil, Sang Kyu Lee, Ningaraddi S. Belavagi, Imtiyaz Ahmed Khazi, Youngjong Kang Two novel conjugated polymers P1, P2 containing dithienothiadiazole[3,4-c]pyridine acceptor and benzodithiophene, naphthodithiophene donors were synthesized by Stille reaction. The polymers were characterized by 1H NMR, GPC, and elemental analysis. The optical band gaps for P1, P2 were found to be 1.67 and 1.60eV. The electrochemical studies of P1, P2 revealed the HOMO and LUMO energy levels of the polymer were −5.07, −5.13eV, and −3.40, −3.53eV respectively. The polymers are thermally stable up to 380–405°C. Optoelectronic investigation and electrical properties of fabricated organic field effect transistor (OFET) suggest these polymers can be potential candidates for organic solar cell application. Graphical abstract image
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2-Ethynylperylene and improved synthesis of 3-ethynylperylene ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Alexey A. Chistov, Sergey V. Kutyakov, Alexey V. Ustinov, Ilya O. Aparin, Anton V. Glybin, Irina V. Mikhura, Vladimir A. Korshun 3-Ethynylperylene 1, an important precursor for fluorescent dyes, fluorescent nucleosides, and potent nucleoside-based antivirals, has been prepared from perylene on a multigram scale (3 steps, 55% overall yield). A simple synthesis of 2-ethynylperylene 2 from perylene (5 steps, 20% yield) has been developed. UV and fluorescence spectra of the ethynylperylenes 1 and 2 are compared to those of perylene. Graphical abstract image
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One-pot, four-component synthesis of new 3,4,7,8-tetrahydro-3,3-dimethyl-11-aryl-2H-pyridazino[1,2-a]indazole-1,6,9(11H)-triones and 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-triones using an acidic ionic liquid N,N-diethyl-N-sulfoethanammonium chloride ([Et3N–SO3H]Cl) as a highly efficient and recyclable catalyst ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Behjat Pouramiri, Esmat Tavakolinejad Kermani A rapid and efficient one-pot, four-component protocol for the synthesis of novel 2H-pyridazino[1,2-a]indazole-1,6,9(11H)-triones (6) and 2H-indazolo[2,1-b]phthalazine-1,6,11-triones (7) has been developed using a stable and reusable Brønsted acidic ionic liquid N,N-diethyl-N-sulfoethanammonium chloride ([Et3N–SO3H]Cl). A range of diverse aldehydes were successfully applied and the corresponding products obtained in good to excellent yields without any by-products. Graphical abstract image
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Palladium(0)-mediated cyclization-coupling of β,γ-unsaturated oximes and aryl iodides ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Joshua Mikesell, Michael D. Mosher The tandem palladium(0)-mediated nucleometalation-cross coupling of β,γ-unsaturated oximes with aryl iodides has been shown to provide the expected 3,5-disubstituted 2-isoxazolines in acceptable yields (11–78%). The addition of a weak base is required for product formation. Some influence on the yield of the reaction is noted in the electronic character of the aryl iodide used in the reaction. Exploration of the substitution patterns on the reactants has led to a proposed mechanism involving a palladium(II)-catalyzed nucleometalation/cyclization followed by reductive elimination of palladium(0) with concomitant coupling to an arene. Graphical abstract image
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Simple synthesis of 4-cyanoquinoline N-oxides ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Robert Bujok, Zbigniew Wróbel, Krzysztof Wojciechowski 4-Cyanoquinoline-N-oxides were obtained in the reactions of 2-nitrobenzylcyanide carbanions with acrylonitrile. Graphical abstract image
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Reinvestigation of acetylation of 3,4-dihydroxybenzaldehyde and reconciliation of previously reported analytical data ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Carlos Berenguer Albiñana, John J. Hayward, Tomas Hudlicky, Ales Machara Acetylation of 3,4-dihydroxybenzaldehyde was reinvestigated. The results in the regiochemical outcome were analyzed in detail by NMR methods and compared with previously published data. Graphical abstract image
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Polyfunctional 4-quinolinones. Synthesis of 2-substituted 3-hydroxy-4-oxo-1,4-dihydroquinolines ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): María S. Shmidt, Isabel A. Perillo, Alicia Camelli, María A. Fernández, María M. Blanco We present here two new methods based on rearrangement reactions to obtain novel 2-substituted 3-hydroxy-4-oxo-1,4-dihydroquinolines, an important family of heterocycles with potential applications. Alkyl 3-hydroxy-4-oxo-1,4-dihydroquinoline-2-carboxylates were obtained by alkoxide promoted rearrangement of alkyl isatinacetates. A second synthetic route involves the alkoxide promoted reaction of both isatin and N-methylisatin, with alkylating agents having acidic methylenes. This reaction leads to the formation of spiroepoxyoxindoles via Darzens’ condensation. When phenacyl bromides are used, the initially obtained benzoyl substituted spiroepoxyoxindoles were smoothly transformed into the corresponding 2-benzoyl-3-hydroxy-4-quinolinones with good to excellent yields. Graphical abstract image
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Br2 as a novel Lewis acid catalyst for Friedel–Crafts alkylation of indoles with α,β-unsaturated ketones ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Deqiang Liang, Xiangguang Li, Wanshun Zhang, Yanni Li, Mi Zhang, Ping Cheng The inexpensive Br2 can serve as a novel Lewis acid catalyst for Friedel–Crafts alkylation of indoles with α,β-unsaturated ketones. Under the catalysis of only 3mol% of Br2, this Michael addition proceeded smoothly with high efficiency and broad substrate scope. Moreover, theoretical calculations suggested that Br2 possesses only the modest power to activate chalcones and is inferior to most tested acids, indicating that acidity might not be the primary cause for the unique activity of Br2 in the current communication. Graphical abstract image
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Synthesis and free radical scavenging activity of 2-alkyl/arylchalcogenyl-N-(4-aryl-1,3-thiazol-2-yl)acetamide compounds ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Lucas Wolf, Natália Quoos, João C.P. Mayer, Diego de Souza, André C. Sauer, Luana Meichtry, Vandreza Bortolotto, Marina Prigol, Oscar E.D. Rodrigues, Luciano Dornelles The synthesis of a new series of organochalcogen-derivatives, 2-alkyl/arylchalcogenyl-N-(4-aryl-1,3-thiazol-2-yl)acetamides 5a–r, provided products in satisfactory yields, which varied from 42% to 95%. All these novel compounds were screened for their in vitro free radical scavenging activity against 2,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals. Compounds 5 (m, h, i, f, q, g, l, c, n) were effective scavengers against the ABTS radical species but less effective on scavenging the DPPH radical, indicating that the antioxidant effect of these compounds were related to protonated radical scavenger activity. Graphical abstract image
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Nucleophilic aromatic substitution of heterocycles using a high-temperature and high-pressure flow reactor ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Manwika Charaschanya, Andrew R. Bogdan, Ying Wang, Stevan W. Djuric We report herein a high-temperature and high-pressure continuous-flow protocol to carry out nucleophilic aromatic substitution (SNAr) of heterocycles with nitrogen nucleophiles. Utilizing the Phoenix Flow Reactor™ in parallel with Design-of-Experiment software enabled rapid optimization of the SNAr protocol. This protocol facilitated efficient synthesis of a broad range of 2-aminoquinazolines, and was extended to 2-aminoquinoxalines and 2-aminobenzimidazoles. Graphical abstract image
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N-Bromo-succinimide promoted synthesis of β-carbolines and 3,4-dihydro-β-carbolines from tetrahydro-β-carbolines ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Santanu Hati, Subhabrata Sen Herein, we report a facile synthesis of 3,4-dihydro-β-carbolines and aromatic β-carbolines from tetrahydro-β-carbolines, mediated by N-bromosuccinimide in toluene at 0°C to room temperature (rt), in good to moderate yields. Graphical abstract image
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Synthesis of 2-amino-substituted-1,3,4-thiadiazoles via 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) mediated intramolecular C–S bond formation in thiosemicarbazones ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Sarangthem Joychandra Singh, Suresh Rajamanickam, Anupal Gogoi, Bhisma K. Patel An effective oxidative intramolecular cyclization (C–S bond formation) of thiosemicarbazones using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has been developed to afford a diverse array of 2-amino-substituted-1,3,4-thiadiazoles. The attractive features of this protocol are operational simplicity, obviates the need of expensive transition-metal catalysts and broad substrate scope. Graphical abstract image
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Synthesis, structure, and properties of a mononuclear ferrocenophane bearing two carbodiimide units as bridges ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Antonia Sola, Raúl A. Orenes, Alberto Tárraga, Pedro Molina A novel bis(carbodiimido)[11]ferrocenophane was synthesized using a methodology involving an aza, Wittig reaction of the 1,1′-bis(triphenylphosphoranylideneamino)ferrocene with the commercially available 1,3-bis(2-isocyanatopropan-2-yl)benzene. Moreover, its electrochemical and chemical properties were also examined. The ureido derivative formed when the bis(carbodiimido)ferrocenophane was hydrolyzed under acidic conditions, behaves as a chemodosimeter for sensing nitrite anions in aqueous solutions. Graphical abstract image
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Concise enantioselective synthesis of (+)-sertraline and (−)-CP-52002 using proline catalysis ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Rupali Kalshetti, V. Venkataramasubramanian, Sanjay Kamble, Arumugam Sudalai A short enantioselective synthesis of (+)-sertraline and its C4 epimer (−)-CP-52002 with an overall yield of 30%, respectively, as its hydrochloride has been described. The key steps are the proline catalyzed Mannich reaction of acetaldehyde and acid catalyzed intramolecular Friedel–Crafts’ alkylation reaction of olefin proceeding with high optical purities. Graphical abstract image
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Keeping it small, polar, and non-flat: diversely functionalized building blocks containing the privileged 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]- and [1,5-a]pyridine cores ()
Publication date: 2 March 2016 Source:Tetrahedron Letters, Volume 57, Issue 9 Author(s): Alexander Mishchuk, Natalia Shtil, Mykola Poberezhnyk, Konstiantyn Nazarenko, Timur Savchenko, Andrey Tolmachev, Mikhail Krasavin Six sets of functionalized building blocks based on 5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridine as well as 5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-a]pyridine cores have been prepared. These compounds are non-flat, bicyclic heterocycles that are likely to find utility as privileged motifs for lead-like compound design. One set of building blocks, (5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-a]pyridin-6-ylmethyl)amines, proved useful as a scaffold for developing compounds that stimulate glucagon-like peptide-1 (GLP-1) secretion and are novel anti-diabetes drug leads. Graphical abstract image
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Editorial board ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8
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Recent advances in transition metal (Pd, Ni)-catalyzed C(sp3)H bond activation with bidentate directing groups ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Xinglin Yang, Gang Shan, Liguo Wang, Yu Rao In recent years, transition metal-catalyzed C(sp3)H functionalization has gradually emerged as a practical and powerful tool to prepare highly valuable chemicals. In this mini-review, we will give some examples to cover recent research advances on transition-metal (Pd, Ni) catalyzed C(sp3)H functionalization via bidentate directing group coordination. Different bidentate directing groups will be discussed. As the whole field of transition metal-catalyzed C(sp3)H functionalization keeps moving forward, more synthetically useful chemo-, regio-, diastereo-, and enantioselective reactions catalyzed by transition-metal with bidentate directing group coordination will be discovered in the future and this promising and attractive strategy will play a more critical role in modern organic synthesis. Graphical abstract image
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Phosphine- and copper-free palladium catalyzed one-pot four-component carbonylation reaction for the synthesis of isoxazoles and pyrazoles ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Nasser Iranpoor, Habib Firouzabadi, Elham Etemadi-Davan The palladium catalyzed one-pot synthesis of isoxazoles and pyrazoles from aryl iodides, terminal alkynes, chromium hexacarbonyl and hydroxylamine hydrochloride or aqueous hydrazine solution is described. The Sonogashira carbonylative coupling intermediate was trapped in situ by hydroxylamine hydrochloride or aqueous hydrazine to deliver isoxazoles or pyrazoles, respectively, in high yields. This efficient method proceeds at atmospheric pressure and moderate temperature and does not require the use of copper, phosphine ligands or gaseous carbon monoxide. Graphical abstract image
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An efficient, three-component synthesis of isoindolin-1-one-3-phosphonates under mild and solvent-free conditions ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Mehdi Adib, Ehsan Sheikhi, Rozita Yazzaf, Hamid Reza Bijanzadeh, Peiman Mirzaei An efficient and mild three-component synthesis of isoindolin-1-one-3-phosphonates is described. The reaction between a 2-formylbenzoic acid, a primary amine, and a trialkyl phosphite proceeded at ambient temperature under catalyst- and solvent-free conditions to afford the desired compounds in excellent yields. Graphical abstract image
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Synthesis of novel chiral biquinolyl diphosphine ligand and its applications in palladium-catalyzed asymmetric allylic substitution reactions ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Rui Zhang, Bin Xie, Guo-Shu Chen, Liqin Qiu, Yi-Xin Chen A novel chiral diphosphine ligand, 6,6′-bis(diphenylphosphino)-5,5′-biquinoline (BIQAP) was synthesized via two step reactions using optical pure BIQOL as starting material and the molecular structure of (R)-BIQAP was determined by single-crystal X-ray diffraction. The ligand was used for Pd-catalyzed asymmetric allylic substitution reactions. High enantioselectiveties were obtained in the corresponding C–C and C–N bond formation of 1,3-diphenyl-2-propenyl acetate, with dimethyl malonate (up to 94% ee) and with potassium phthalimide (up to 96% ee). Graphical abstract image
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Development of a simple system for the oxidation of electron-rich diazo compounds to ketones ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Nicholas R. O’Connor, Peter Bolgar, Brian M. Stoltz Mild heating of diazo compounds in DMSO furnishes ketone products in moderate to excellent yields. The reaction is particularly effective on electron-rich substrates and exhibits high chemoselectivity, allowing for the use of diazo compounds containing additional oxidation-prone functional groups. This straightforward protocol offers an alternate route to synthetically useful α-ketoesters from readily available aryl diazoacetates. Graphical abstract image
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Polymer monolith-supported dirhodium(II)-catalyzed continuous flow cyclopropanation in capillary format† ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Frady G. Adly, Ashraf Ghanem Herein, the first trial for the miniaturization of the dirhodium(II)-catalyzed cyclopropanation reaction is reported. Rh2(S- tert PTTL)4 † This catalyst (patent PCT/AU2015/000557) is available at Strem Chemicals. † was immobilized inside a capillary microreactor on a pyridine-derived monolithic support. The system demonstrated good stability with low leaching rate of the dirhodium(II) catalyst comparable to conventional packed solid support. The Rh2(S- tert PTTL)4-catalyzed cyclopropanation microreaction was carried out under continuous flow conditions generating the cyclopropane product in moderate yield (44%) and excellent diastereoselectivity (>20:1 E:Z dr). Graphical abstract image
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Aplysiasecosterols B and C: two new 9,11-secosteroids with a cis-fused 1,4-quinone structure from the sea hare Aplysia kurodai ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Masaki Kita, Atsushi Kawamura, Hideo Kigoshi Two new 9,11-secosteroids with a cis-fused 3β,5β-dihydroxy-1,4-quinone structure, aplysiasecosterols B and C, were isolated from the sea hare Aplysia kurodai. Their structures were determined by 1D- and 2D-NMR spectroscopic analysis, molecular modeling studies, and a modified Mosher’s method. Aplysiasecosterol B might be the biosynthetic precursor of aplysiasecosterol A, another 9,11-secosteroid with a tricyclic γ-diketone structure from A. kurodai, via two α-ketol rearrangements and intramolecular acetalization. Graphical abstract image
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An alternate synthesis of appetite suppressant (R)-2-benzylmorpholine employing Sharpless asymmetric epoxidation strategy ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): N. Viswanadh, P. Mujumdar, M. Sasikumar, S.S. Kunte, M. Muthukrishnan An alternate synthesis of (R)-2-benzylmorpholine 1, an appetite suppressant agent has been accomplished starting from readily available trans-cinnamyl alcohol employing Sharpless asymmetric epoxidation strategy as a key step, with an overall yield of 24%. Graphical abstract image
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Three-component reductive alkylation of 2-hydroxy-1,4-naphthoquinones with lactols ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Eliana E. Kim, Evans O. Onyango, Jennifer R. Pace, Timothy M. Abbot, Liangfeng Fu, Gordon W. Gribble Lactols II, obtained by DIBAL reduction of their corresponding lactones I, in equilibrium with their hydroxyaldehyde tautomers III were used in a three-component reductive alkylation with 2-hydroxy-1,4-naphthoquinone to give a series of 3-alkylated 2-hydroxy-1,4-naphthoquinone derivatives IV. Graphical abstract image
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Semisynthesis of membrane-anchored cholesteryl lipoproteins on live cell surface by azide–alkyne click reaction ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Balázs Schäfer, Erika Orbán, Gabriella Fiser, Annamária Marton, Csaba Vizler, Csaba Tömböly Cholesteryl lipoprotein semisynthesis was accomplished via a copper-catalyzed azide–alkyne cycloaddition on the surface of live cells. In this convergent synthesis an azido-cholesterol was introduced into the cell membrane without the application of detergents followed by conjugation of the C-terminal alkyne modified protein. This cytocompatible method resulted in a folded membrane-anchored protein containing a small molecule fluorophore in the lipid headgroup. Graphical abstract image
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Total syntheses and structure–activity relationship study of parthenolide analogues ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Jing Long, Ya-Hui Ding, Pan-Pan Wang, Quan Zhang, Yue Chen Two new parthenolide analogues were obtained by total synthesis and assayed for their in vitro anticancer activities to study their structure–activity relationship. Based on the structure and anticancer activity results, two new SAR can be drawn: (1) replacement of the lactone moiety with lactam moiety greatly decreased the anticancer activity; (2) the C-14 methyl group of parthenolide might be important for its high anticancer activity. Graphical abstract image
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A novel azo-thiourea based visible light switchable anion receptor ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Ying-Xue Yuan, Liang Wang, Yi-Fei Han, Fen-Fang Li, Hong-Bo Wang A novel azo-thiourea based anion receptor can be synthesized by coupling a bis-azoaniline motif with butyl isothiocyanate with 45% yield under mild conditions. It was found that azo-thiourea was an excellent receptor to recognize various di-carboxylate anions. It can serve as a colorimetric sensor for azelate ion and led to a significant change in the absorption spectrum. Furthermore, a reversible trans–cis isomerization of azo-thiourea induced by visible lights was confirmed by 1H NMR spectroscopy. Graphical abstract image
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Dithiocarbamates as an efficient intermediate for the synthesis of 2-(alkylsulfanyl)thiazoles in water ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Azim Ziyaei Halimehjani, Leila Hasani, M. Ali Alaei, Mohammad R. Saidi A simple, green and high-yielding procedure for the synthesis of 4-substituted-2-(alkylsulfanyl)thiazoles from the reaction of dithiocarbamates and α-halocarbonyl containing compounds in water is described. Also, a one-pot, two-step procedure for the synthesis of 2-(alkylsulfanyl)thiazoles from acetophenone and dithiocarbamates was developed. Graphical abstract image
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Microwave assisted synthesis and cytotoxic activity evaluations of new benzimidazole derivatives ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Hue Thi Buu Bui, Quy Thi Kim Ha, Won Keun Oh, Duy Duc Vo, Yen Nguyen Tram Chau, Cuc Thi Kim Tu, Em Canh Pham, Phuong Thao Tran, Loan Thi Tran, Hieu Van Mai Twelve new 2-quinolizinylbenzimidazole and 2-naphthalylbenzimidazole derivatives with various 5- and 6-positioned substituents (aza, H, CH3, Cl, NO2, NH2, OCH3), have been synthesized in moderate to excellent yields via the condensation of 4-oxo-4H-quinolizinecarbaldehyde or naphthalenecarbaldehyde with substituted o-phenylenediamines, o-nitroaniline, and 2,3-pyridinediamine using sodium metabisulfite or sodium hydrosulfite under microwave irradiation. The new benzimidazole derivatives were screened for their cytotoxic activity against the human breast cancer cell line (MCF-7). The results showed on one hand that 2-(substituted quinolizinyl)-1H-benzimidazoles (12b–f) were less active (3–6fold) than the positive control Tamoxifen (CC50 =6.52μM), and on the other hand, among the 2-(substituted naphthalyl)-1H-benzimidazoles series (13a–f), compounds 6,7,8-trimethoxy-3-(5-chloro-1H-benzo[d]imidazol-2-yl)naphthalen-1-ol (13c) (CC50 =7.48μM) and 6,7,8-trimethoxy-3-(5-methoxy-1H-benzo[d]imidazol-2-yl)naphthalen-1-ol (13f) (CC50 =6.43μM) were found to be as active as Tamoxifen. Graphical abstract image
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Selacyclicbiflavone A, an unusual macrocyclic biflavone from Selaginella uncinata (Desv.) Spring ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Hui Zou, Ping-Sheng Xu, Rui Liu, Zhen-Xing Zou, Jing Li, Ai-Guo Zhong, Jian-Zhong Hu, Kang-Ping Xu, Gui-Shan Tan An unusual macrocyclic biflavone, selacyclicbiflavone A (1), have been isolated from Selaginella uncinata. The structure was elucidated on the basis of rigorous spectroscopic analysis including 1D and 2D NMR experiments as well as HRESIMS techniques. The absolute stereochemistry of compound 1 was further confirmed by comparing experimental data with calculated electronic circular dichroism (ECD) spectra. This is the first report of the macrocyclic biflavone with an unprecedented methylene bridge. A possible biosynthetic pathway was also postulated. Graphical abstract image
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Efficient and chromatography-free methodology for the modular synthesis of oligo-(1H-pyrazol-4-yl)-arenes with controllable size, shape and steric bulk ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Laurence J. Kershaw Cook, Rachel Kearsey, Jessica V. Lamb, Edward J. Pace, Jamie A. Gould A novel methodology to synthesise oligo-(1H-pyrazol-4-yl)-arenes with controllable size, shape and steric bulk from 1-trityl-1H-pyrazol-4-ylboronate pinacol esters. This straightforward and efficient procedure can be applied to a variety of brominated aromatic precursors in a manner which leaves the pyrazole NH intact for further modification or coordination to metal ions. This will enable the synthesis of novel bioactive molecules and molecular material precursors, all achievable without any purification techniques beyond standard extraction and trituration. Graphical abstract image
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Synthesis of enantiopure epoxide by ‘one pot’ chemoenzymatic approach using a highly enantioselective dehydrogenase ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Kai Wu, Lifeng Chen, Haiyang Fan, Zhiqiang Zhao, Hualei Wang, Dongzhi Wei Enantiopure α-phenethyl alcohols, including aromatic halohydrins, are important chiral building blocks. One of the best approaches to synthesise α-phenethyl alcohols is asymmetric reduction of prochiral ketones by alcohol dehydrogenases (ADHs). The obtained enantiopure halohydrin could be directly used to produce enantiopure epoxide through a base-induced ring-closure reaction, which is an attractive ‘one pot’ chemoenzymatic method for producing high-yield epoxide. In this study, a novel medium-chain dehydrogenase (KcDH) from Kuraishia capsulate CBS1993 was identified and characterised to show its broad substrate scope and excellent enantioselectivity. KcDH showed activities on 25 substrates of the 26 tested aromatic ketones and heteroaryl ketones, with an enantiomeric excess (ee) >99% and the highest relative activity observed with para-nitro acetophenone. Due to its high enantioselectivity for α-haloketones, a chemoenzymatic method for the synthesis of enantiopure styrene oxide (SO) and phenyl glycidyl ether (PGE) was developed through a base-induced ring-closure reaction on enantiopure halohydrin obtained with KcDH. (R)-SO and (S)-PGE were obtained in 86% and 94% analytical yield, respectively, and both epoxides were obtained with ee >99%. Thus, our results suggested that KcDH may be a promising biocatalyst for the production of multiple enantiopure α-phenethyl alcohols and epoxides. Graphical abstract image
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Ion complexation-controlled columnar mesophase of calix[4]arene–cholesterol derivatives with Schiff-base bridges ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Xiaoyi Zhang, Hongyu Guo, Fafu Yang, Jin Yuan Two novel calix[4]arene–cholesterol derivatives 7a and 7b with Schiff-base bridges were synthesized in yields of 70–80%. Their structural and conformational characterization had been achieved by NMR, MS, and elemental analysis. Their mesomorphic behaviors were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. They possess mesomorphic properties with the molecular arrangement of the calixarene bowlic column and Schiff-based cholesterol unit as ancillary lateral column. The complexes of 7a and 7b with AgClO4 showed no mesophase. These results suggested that the mesophase of compounds 7a and 7b could be tuned by the ion-complexation behavior. Graphical abstract image
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Copper-catalyzed regioselective hydroboration of terminal alkynes in aqueous medium ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Zi-Jian Yao, Shibin Hong, Wei Zhang, Mengyan Liu, Wei Deng A mild and environment-friendly copper-catalyzed hydroboration of terminal alkynes in aqueous medium was reported. Regioselectivity control was achieved in the presence of cyclodextrin–bispyridine ligand (CD-1). This protocol was successfully applied to inactivated terminal alkynes. Moreover, the ligand was recovered and reused without any loss of activity over five cycles. Graphical abstract image
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Urea as mild and efficient additive for palladium catalyzed Sonogashira cross coupling reaction ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Manashi Sarmah, Anindita Dewan, Ashim J. Thakur, Utpal Bora A catalytic system based on Pd(OAc)2/urea has been developed for Sonogashira cross coupling of aryl halides with terminal alkynes at room temperature. This catalytic system effectively promotes Sonogashira coupling of both aryl iodides and aryl bromides to give polyfunctional alkynes under copper and amine free conditions. The catalytic system is readily accessible, inexpensive and highly flexible for both aromatic and aliphatic alkynes. Graphical abstract image
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New access to 4-aryl[2,2]paracyclophanes by high-pressure Diels–Alder reaction ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Lucio Minuti, Anna Barattucci, Paola Maria Bonaccorsi, Carlo Siciliano, Andrea Temperini The first synthesis of novel 4-aryl[2,2]paracyclophanes based on the Diels–Alder reaction of 4-carbomethoxyethynyl[2,2]paracyclophane as the dienophile with methyl-1,3-butadienes is described. Activation of the Diels–Alder reactions by high-pressure (8kbar) in combination with the Lewis acid EtAlCl2 allows to obtain in good yield and total regioselectivity the cyclohexadienyl-paracyclophane cycloadducts that are converted to the corresponding aryl-paracyclophanes by DDQ oxidation. Graphical abstract image
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Development of a practical and scalable route for the preparation of the deacetoxytubuvaline (dTuv) fragment of pretubulysin and analogs ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Margherita Brindisi, Samuele Maramai, Alessandro Grillo, Simone Brogi, Stefania Butini, Ettore Novellino, Giuseppe Campiani, Sandra Gemma We present herein a novel and convenient route for the scaling-up of the dTuv fragment of pretubulysin. The newly conceived chemical path involves a practical and efficient one-step procedure for the preparation of a key thiazole intermediate, followed by high-yielding Wittig olefination/reduction steps. The optimized route, starting from the inexpensive and non-toxic l -cysteine, encompasses five synthetic steps and only two chromatographic purifications, thus displaying a dramatically increased overall yield. The versatility of the proposed approach also provides new hints for the exploration of pretubulysin derivatives bearing diverse heterocyclic portions. Graphical abstract image
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Direct chemical derivatization of natural plant extract: straightforward synthesis of natural plant-like hydantoin ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Keisuke Tomohara, Tomohiro Ito, Naoto Hasegawa, Atsushi Kato, Isao Adachi The direct chemical derivatization of natural plant extracts that would enable the straightforward synthesis of natural plant-like molecules seemed to be far from reality due primarily to the inherently complex chemical property of the extract. After model studies, the envisioned derivatization was realized under the rationally designed Bucherer–Bergs reaction conditions to afford unnatural hydantoin with tetrasubstituted carbon from the ethyl acetate extract of Curcuma zedoaria. The reaction proceeded with enough chemoselectivity to identify the desired product from the mixture by the reliable guidance of spectroscopic analyses. Graphical abstract image
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Base catalyzed reaction of ethyl thioglycolate with β-aryl-β-(methylthio) acroleins: a general method for the synthesis of 2-carbethoxy-5-substituted/4,5-annulated thiophenes in high overall yields ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): G. Byre Gowda, C.S. Pradeepa kumara, N. Ramesh, M.P. Sadashiva, H. Junjappa (Methylthio) acroleins 1a–m were shown to be stable unlike their counterpart the chloroacroleins and their efficacy as 1,3-dielectrophilic properties have now been examined successfully in this work. They are shown to react with ethyl thioglycolate in the presence of anhydrous potassium carbonate in boiling ethanol to yield the corresponding 5-substituted/4,5-annulated-2-carbethoxy thiophenes in 70–80% overall high yields. Graphical abstract image
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Substitution nitrogen for chlorine of heptamethine cyanines for large Stokes shift fluorescent probes ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Lihui Zheng, Liqiu Wang, Pengjun Wang, Qi Sun, Xuelong Liu, Xiaobo Zhang, Shaobo Qiu On the basis of syntheses of three heptamethine indocyanines with methyl, ethyl, or p-carboxybenzyl groups on N atoms in the indole rings, nine novel aminoderivatives were designed and synthesized by butylamine, taurine, or benzylamine reacting with the indocyanines for substitution nitrogen for chlorine. The obtained products were purified by SiO2 column chromatography, and confirmed by ESI-MS and 1H NMR. Compared to the parents, the aminoderivatives showed blue shifts, larger Stokes shifts, and stronger fluorescence intensity, which were mainly related to the electron-donating ability of the amino substituents in the aminoderivatives. The stronger electron-donating ability of the amino substituents made the maximum absorption wavelengths show greater blue shifts. Graphical abstract image
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Selective CH functionalization of electron-deficient aromatics by carbamoylsilanes: synthesis of aromatic carbinolamines or amides ()
Publication date: 24 February 2016 Source:Tetrahedron Letters, Volume 57, Issue 8 Author(s): Yanhong Liu, Pei Cao, Jianxin Chen Selective CH functionalization of electron-deficient aromatics with various carbamoylsilanes is developed under catalysts-free conditions. These transformations provide a facile and efficient method for synthesizing some tertiary or secondary aromatic carbinolamines and amides in good yields. Graphical abstract image
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