Tetrahedron Letters

Editorial board ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20
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Graphical Contents List ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20
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Cu-nanoparticles on cellulose/H2O–CH3CN/microwave: a green system for the selective oxidation of alcohols to aldehydes ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Diganta Baruah , Ujwal Pratim Saikia , Pallab Pahari , Dilip Konwar We report a new alternative ligand and additive free recyclable green heterogeneous catalytic system, Cu-nanoparticles on cellulose template that gives efficient and selective aerobic oxidation of a broad range of benzylic alcohols, cinnamyl alcohols, and heteroaryl alcohols to the corresponding aldehydes under microwave irradiation. Use of green solvent, very short reaction time, and recyclability of the catalyst make this protocol highly advantageous. Graphical abstract image
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Reaction of a brominated benzolactone/lactam with 4-methoxythiobenzamide and thiourea: an Eschenmoser coupling reaction, ring transformation, or dimerization? ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Richard Kammel , Denisa Tarabová , Zdeňka Růžičková , Jiří Hanusek The reactions of 3-bromo-1-benzofuran-2(3H)-one (1a) and 3-bromo-1,3-dihydro-2H-indol-2-one (1b) with 4-methoxythiobenzamide and thiourea under mildly basic conditions are reported. While brominated lactone 1a gave the expected 5-(2-hydroxyphenyl)-2-(4-methoxyphenyl)-1,3-thiazol-4-ol (2) or 2-amino-5-(2-hydroxyphenyl)-1,3-thiazol-4(5H)-one (5) products, the analogous brominated lactam 1b reacted with the thioamide via an unexpected Eschenmoser coupling reaction to give (3Z)-3-[amino(4-methoxyphenyl)-methylidene]-1,3-dihydro-2H-indol-2-one (3). When lactam 1b was treated with thiourea, isoindigo (4) was the only isolated product. The reaction mechanisms, involving formation of α-thioiminium or isothiouronium salts and their base-catalyzed decomposition are also proposed. Graphical abstract image
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Copper-catalyzed one-pot tandem reactions toward the synthesis of indoles using o-iodoanilines, acyl chlorides, and Wittig reagents ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Bin Huang , Deqing Hu , Jing Wang , Jie-Ping Wan , Yunyun Liu The one-pot reactions of acyl chlorides, Wittig reagents, and o-iodoanilines involving a copper-catalyzed C–C coupling have been realized to provide various indoles. The reactions proceed on the basis of the in situ generation of allenes to incorporate o-iodoanilines via tandem Michael addition, C–C coupling, and tautomerization to afford indoles. This direct one-pot protocol allows the synthesis of indoles with all easily available materials. Graphical abstract image
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Bis(acetylacetonato)copper(II) catalyzed oxidative cross-dehydrogenative coupling (CDC) for the synthesis of α-acyloxy ethers through direct activation of α-C(sp3)–H bond of cyclic ether ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Dhrubajyoti Talukdar , Suchibrata Borah , Mihir K. Chaudhuri A bis(acetylacetonato)copper(II)catalyzed convenient protocol has been developed for the synthesis of α-acyloxy ethers via cross-dehydrogenative coupling (CDC) using tertiary-butylhydroperoxide (TBHP) as the oxidant. A radical mechanism is suggested for the reaction. Graphical abstract image
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Copper-catalyzed cross-dehydrogenative coupling of N-arylacrylamides with chloroform using tert-butyl peroxybenzoate as oxidant for the synthesis of trichloromethylated 2-oxindoles ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Chun-Wo Chan , Pui-Yiu Lee , Wing-Yiu Yu A Cu-catalyzed cross-dehydrogenative coupling of N-arylacrylamides with chloroform is achieved using tert-butyl peroxybenzoate as oxidant, and trichloromethylated oxindoles were obtained in excellent yield and regioselectivity. This reaction should proceed by cascade CCl3 radical CC addition and aryl cyclization. Graphical abstract image
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Knoevenagel condensation of aromatic bisulfite adducts with 2,4-thiazolidinedione in the presence of Lewis acid catalysts ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Sandeep Mohanty , Amrendra Kumar Roy , G. Sandeep Reddy , K.P. Vinay Kumar , B. RamaDevi , G. Bhargavi , Arun Chandra Karmakar Several commercial Lewis acids, specifically TiCl4, were able to promote the condensation reaction between aromatic bisulfite adducts and 2,4-thiazolidinedione to produce 5-arylidene derivatives. The product distribution was not affected by the equivalents of TiCl4 used, but was dependent on temperature and the nature of the solvent medium. In all cases, the reaction required activation of the aromatic bisulfite adducts by Lewis acids, followed by the loss of SO2 and subsequent regeneration of the parent aldehyde. The in situ formed aldehyde ultimately underwent acid-catalyzed carbon–carbon bond formation to give 5-arylidene derivatives. The reaction with TiCl4 afforded the products from aromatic and aliphatic bisulfite adducts in moderate to good yields. When hydrated Lewis acids were used, in addition to 5-arylidenes, the in situ formed aldehyde underwent a disproportionation reaction to give a carboxylic acid as a by-product. Graphical abstract image
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Total synthesis of (±) Xyloketal H ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Viraj A. Bhosale , Mukund G. Kulkarni An efficient total synthesis of (±) Xyloketal H is described, the Wittig olefination–Claisen rearrangement protocol has served here as the key transformation for constructing the core structure of the metabolite. Graphical abstract image
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Exploiting photoredox catalysis for the synthesis of tetra- and di-hydrofurans ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Gabriele Fumagalli , Scott Boyd , Michael F. Greaney Tetra- and di-hydrofuran heterocycles can be synthesised in a single step through the addition of functionalised alkyl bromides to styrene derivatives under photoredox catalysis. Graphical abstract image
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The synthesis, physicochemical properties, and electrochemical polymerization of fluorene-based derivatives as precursors for conjugated polymers ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Ammar Khelifa Baghdouche , Mounia Guergouri , Salima Mosbah , Lotfi Benmekhbi , Leila Bencharif Two novel monomers, 2,7-bis[(thien-2-yl)cyanovinyl]-9,9-dipentylfluorene (FPT) and 2,7-bis-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)cyanovinyl]-9,9-dipentylfluorene (FPE) are synthesized and their electrochemical polymerization is achieved via potentiostatic methods. The corresponding polymers, poly(2,7-bis[(thien-2-yl)cyanovinyl]-9,9-dipentylfluorene) (PFPT) and poly(2,7-bis[(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)cyanovinyl]-9,9-dipentylfluorene) (PFPE), are characterized by cyclic voltammetry, FT-IR, and UV–vis spectroscopy. The band gap values (E g) of the polymers are found to be 2.21 and 1.92eV for PFPT and PFPE, respectively. Graphical abstract image
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Al(OTf)3-catalyzed SN2′ substitution of the β-hydroxy group in Morita–Baylis–Hillman adducts with indoles ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Mukut Gohain , Shunhuang Lin , Barend C.B. Bezuidenhoudt The Al(OTf)3-catalyzed SN2′-type substitution of the β-hydroxy group in Morita–Baylis–Hillman adducts with indoles is reported. The reaction proceeded efficiently with aryl-, heteroaryl-, aliphatic- and alicyclic-containing β-hydroxyketones and a variety of substituted indoles. Graphical abstract image
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Synthesis of substituted carbamo(dithioperoxo)thioates as potential BCA2-inhibitory anticancer agents ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Vincenzo Cilibrasi , Kwok Tsang , Matteo Morelli , Francesca Solfa , Helen L. Wiggins , Arwyn T. Jones , Andrew D. Westwell A new, simple, one-step synthetic route to carbamo(dithioperoxo)thioates from commercially available starting materials is described. The key step of this new synthetic approach involves the tetrabromomethane-promoted reaction between secondary amines, carbon disulfide and alkyl thiols under basic conditions at room temperature. New compounds from this series selected for anticancer screening showed selective sub-micromolar activity within BCA2-expressing human breast cancer cell lines. Graphical abstract image
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Styryl-based NLO chromophores: synthesis, spectroscopic properties, and theoretical calculations ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Ergin Yalçın , Sylvain Achelle , Yasmina Bayrak , Nurgül Seferoğlu , Alberto Barsella , Zeynel Seferoğlu A novel series of styryl-based chromophores is synthesized, the constituents of which are characterized by UV–Vis, NMR, mass spectrometry, and thermal analysis. The chromophores show good solubility in MeOH, THF, and CH2Cl2. They also show good thermal stability for practical applications. Density functional theory calculations are employed in order to ascertain the structural, molecular, and electronic properties of the dyes. Moreover, the second order nonlinear optical (NLO) responses of the dyes are measured by the electric field induced second harmonic (EFISH) generation method. Relatively high scalar products of the vector component of the first hyperpolarizability tensor and the dipole moment vector (μβ) are obtained for some of the compounds. Graphical abstract image
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Direct synthesis of imidazolidin-4-ones via cycloadditions of imines with a Leuchs’ anyhdride ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Bilgesu Onur Sucu , Nuket Ocal , Ihsan Erden A new method for a one-step synthesis of imidazolidin-4-ones has been developed based on tandem nucleophilic additions-decarboxylation-intramolecular cyclizations of imines with a Leuchs’ anhydride. Depending on the reaction conditions (with or without base), one either obtains the title compounds, or α-amino acid amide-derived Schiff bases. The latter have also been shown as useful precursors of α-amino acid amides by selective reduction of the imine bond with NaBH4 in the presence of p-TsOH. Graphical abstract image
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Copper-catalyzed site-selective S–S and C–C homocoupling of α-enolic dithioesters: straightforward and efficient access to 1,2-dithiols ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): B. Janaki Ramulu , Anugula Nagaraju , Sushobhan Chowdhury , Suvajit Koley , Maya Shankar Singh An operationally simple, economical, and practical new method for the synthesis of highly functionalized 1,2-dithiols has been developed by copper catalyzed self-coupling of α-enolic dithioesters via consecutive formation of S–S and C–C bonds. Low-cost copper powder together with Ag2O as oxidant and promoter can be recycled at least four times with no loss of catalytic activity, making this strategy an ideal alternative to existing methods. Notably, in situ formation of S,S′-bis(dithioacetal) as a reactive intermediate has been proven, and the corresponding mechanistic insights are experimentally established. Graphical abstract image
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Preparation of azide biosynthetic surrogates of myo-inositol ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Sandip Pasari , Shareef M. Ismail , Markus R. Wenk , Martin J. Lear As a prelude to biomolecular incorporation studies, practical routes to a series of four regioisomeric azido-deoxy derivatives of inositol that mimic the natural myo-stereochemistry are described. Starting from commercially available myo-inositol, the regioselective and stereoselective introduction of azide functionality was achieved at the C-2, C-3, C-4, and C-5 positions via azide displacement of the corresponding O-sulfonates of suitably protected scyllo-, chiro-, epi-, and neo-inositols, respectively. Notably, a final one-pot acetolysis method conveniently allowed for rapid access to pentaacetate azido-deoxy inositols. Investigations on the metabolic incorporation of these myo-inositol azide surrogates in both acetate and free alcohol forms are in progress. Graphical abstract image
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Total synthesis of aplysinoplide B ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Noriki Kutsumura , Kazuhiro Matsuo , Takao Saito The first total synthesis of aplysinoplide B has been achieved. The synthetic highlight of our approach includes sp2–sp3 Suzuki–Miyaura cross coupling of a vinyl bromide with an alkyl 9-BBN derivative. The vinyl bromide was efficiently synthesized from the disubstituted Z-alkene utilizing a one-pot regioselective bromination. Through the synthetic studies, the absolute stereochemistry at the C4 position of naturally occurring aplysinoplide B was established as an R configuration. Graphical abstract image
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Acid catalyzed nitrile thiolysis of 3-amino-acrylonitriles, toward the synthesis of 3,4-substituted-5-amino-isothiazoles ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Steven L. Kuklish , Ryan T. Backer , Matthew J. Fisher , Aaron M. Kempema , Scott C. Mauldin , Alain Merschaert Application of an acid-catalyzed thioamidation of β-amino-acrylonitriles to the corresponding β-amino-thioacrylamides toward the synthesis of 3,4-substituted-5-amino-isothiazoles is described. The greatest yields were observed for examples with electron rich aromatic systems. This method uses inexpensive and easily handled reagents. Graphical abstract image
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Asymmetric synthesis of (S)- and (R)-norketamine via Sharpless asymmetric dihydroxylation/Ritter amination sequence ()
Publication date: 13 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 20 Author(s): Manfred Biermann , Guangrong Zheng , Marhaba Hojahmat , Nick V. Moskalev , Peter A. Crooks Asymmetric synthesis of (S)-norketamine and (R)-norketamine utilizing Sharpless asymmetric dihydroxylation followed by stereo-controlled Ritter amination and Jones oxidation is reported. This method allowed the preparation of the free base of (S)-norketamine and (R)-norketamine in pure crystalline form for the first time. The absolute configuration of both enantiomers was verified by X-ray structure and optical resolution of racemic norketamine. Graphical abstract image
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Editorial board ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19
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Graphical Contents List ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19
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High valent FeIV chemistry in sustainable oxidation catalysis ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Preeti P. Chandrachud , David M. Jenkins Recent research in oxidation catalysis has focused on employing first-row metals with a lower environmental impact than their traditional counterparts. Iron is particularly suited for this task since the discovery of isolable non-heme iron(IV) complexes over a decade ago. This Letter summarizes the developments in the last decade for oxidation of organic substrates that proceed through iron(IV) intermediates. Eight separate oxidation reactions are reviewed. Graphical abstract image
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Terminal ynamides: synthesis, coupling reactions, and additions to common electrophiles ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Andrea M. Cook , Christian Wolf Ynamides consist of a polarized triple bond that is directly attached to a nitrogen atom carrying a sulfonyl, an alkoxycarbonyl, an acyl, or another electron withdrawing group. The triple bond polarization renders ynamides broadly useful building blocks with synthetic opportunities that go far beyond traditional alkyne chemistry. The versatile reactivity of ynamides in cycloadditions, cycloisomerizations, regioselective additions with various nucleophiles or electrophiles, ring-closing metathesis, and many other reactions has been investigated in detail during the past decades. A common feature of these methods is that the triple bond is consumed and either cleaved or transformed to a new functionality. The wealth of reports on these ynamide reactions is in stark contrast to the dearth of carbon–carbon bond formations that leave the triple bond of terminal ynamides intact. The recent introduction of effective synthetic methods for the preparation of terminal ynamides has set the stage to fully explore the synthetic potential of this intriguing class of compounds. This digest Letter summarizes the most effective routes to terminal ynamides and the current state of selective nucleophilic addition, substitution, and coupling reactions, including the first examples of asymmetric synthesis. Graphical abstract image
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Highly palladium catalyzed chemoselective domino reaction: a practical way to the synthesis of 6H-benzo[c]chromenes and spiro[benzo[c]chromene-6,2′-chroman]s ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Feijun Wang , Yunlong Liu , Feng Chen , Mingliang Qu , Min Shi A domino palladium-catalyzed hydrogenation reaction was developed to construct 6H-benzo[c]chromene scaffold. Using Pd/C catalyst under H2 balloon, 6H-benzo[c]chromenes were obtained in nearly quantitative yields. However, using Pd(PhCN)2Cl2/DPEphos/AgBF4 as the catalytic system, spiro[benzo[c]chromene-6,2′-chroman]s were obtained in up to 91% yields. Graphical abstract image
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Efficient access to functionalized cyclobutanone derivatives using cyclobuteniminium salts as highly reactive Michael acceptors ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Alexandre Lumbroso , Saron Catak , Sarah Sulzer-Mossé , Alain De Mesmaeker A new efficient access to β-substituted cyclobutanones via Michael addition using cyclobuteniminium salts is described. Competition reactions have been performed in order to demonstrate the higher reactivity of cyclobuteniminium salts compared to their cyclobutenone analogs and the results have been rationalized by DFT calculation. Michael adducts have also been efficiently functionalized demonstrating the utility of such building blocks in organic synthesis. Graphical abstract image
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Regioselective C2-lithiation of N-Boc-3-bromopyrroles: a novel approach towards the synthesis and scale-up of 3-(2-formyl-4-methyl-1-H-pyrrol-3-yl)propanoic acid ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Donghua Dai , Bhaskar Rao Venepalli ortho-Lithiation of N-Boc-3-bromopyrroles (7b, 7d) with LDA in THF at −75°C, followed by reactions with ethyl formate gave exclusive C2-formylpyrroles (9b, 9c, 9d, 9e) in good yields. This methodology was applied to the synthesis of 3-(2-formyl-4-methyl-1-H-pyrrol-3-yl)propanoic acid (4a), a penultimate precursor to SU5402. The process for making 4a has also been optimized which involves a non-chromatography eight-step synthesis with an overall 18% yield. Graphical abstract image
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Selective aldol condensation or cyclotrimerization reactions catalyzed by FeCl3 ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Renzo Arias-Ugarte , Francis S. Wekesa , Michael Findlater The inexpensive and commercially available FeCl3 catalyzes the selective homo-aldol condensation of aldehydes into the corresponding α–β unsaturated aldehydes, presumably through an unobserved aldol intermediate. Surprisingly the reaction course can be diverted to produce 1,3,5-trioxanes via aldehyde cyclotrimerization. Selectivity for trioxanes is achieved at lower temperatures and is enhanced by the presence of water, contrary to prior reports. A broad range of aliphatic and aromatic aldehydes are capable of undergoing these transformations; short reaction times, high yields, scalability, and easy purification processes are also described. Graphical abstract image
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Bromodimethylsulfonium bromide: an efficient catalyst for one-pot synthesis of 4-phenacylidene flavene derivatives ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Suchandra Bhattacharjee , Deb K. Das , Abu T. Khan The synthesis of 4-phenacylidene flavenes (3) was accomplished by a one-pot pseudo three-component condensation reaction between salicylaldehydes and acetophenones in the presence of 20mol% of bromodimethylsulfonium bromide (BDMS) in acetonitrile at room temperature. The attractive features of this protocol are: use of organo-catalyst BDMS, simple reaction procedure, high bond-forming efficiency, good yields, and environmentally benign reaction conditions. Graphical abstract image
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Copper-catalyzed tandem synthesis of 2-(sulfonylimino)alkanamides from N-sulfonylketenimines and alkyl isocyanides ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Issa Yavari , Majid Ghazanfarpour-Darjani , Manijeh Nematpour Ketenimine intermediates, generated by the addition of copper acetylides to tosyl azides, are trapped by alkyl isocyanides to yield N-alkyl-2-(sulfonylimino)alkanamides in moderate to good yields. Graphical abstract image
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Synthesis of (E)-nitroolefins and substituted nitrobenzenes via decarboxylative nitration using cellulose supported copper nanoparticles ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Diganta Baruah , Pallab Pahari , Dilip Konwar The first cellulose supported copper nanoparticles catalyzed decarboxylative nitration of cinnamic and benzoic acids are described. (E)-Nitroolefins were obtained stereoselectively in excellent yields under mild and convenient reaction conditions in the case of cinnamic acids. This novel and efficient catalytic system was also successfully applied in nitrodecarboxylation of a few benzoic acids which is one of the major advantages over the existing protocols. Graphical abstract image
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Expedient stereoselective synthesis of new dihydropyrano- and dihydrofuranonaphthoquinones ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Tuyet Anh Dang Thi , Yves Depetter , Karen Mollet , Hoang Thi Phuong , Doan Vu Ngoc , Chinh Pham The , Ha Thanh Nguyen , Thu Ha Nguyen Thi , Hung Huy Nguyen , Matthias D’hooghe , Tuyen Van Nguyen Heterocyclic naphthoquinones represent valuable scaffolds in medicinal chemistry. In the present Letter, the efficient stereoselective synthesis of new dihydropyrano- and dihydrofuranonaphthoquinones by means of one-pot multicomponent reactions using 2-hydroxy-1,4-naphthoquinone, an aromatic aldehyde and ethyl 4,4,4-trifluoroacetoacetate or a pyridinium bromide, respectively, is described. Graphical abstract image
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Biaryl thioether synthesis via CuI catalyzed dominothiolation of aryl halides in the presence of DMAP as ligand ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Subhasish Roy , Prodeep Phukan An improved protocol has been developed for the synthesis of symmetrical biaryl sulfides via a dominothiolation reaction using CuI as catalyst in the presence of DMAP as ligand. The coupling reaction of aryl halides was carried out in the presence of 5mol% of CuI and 20mol% of DMAP using thiourea as sulfur transfer agent. High yields of corresponding product were obtained by carrying out the reaction in DMSO at 120°C. Graphical abstract image
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Base-free direct formylation of aromatic iodides using CO2 as C1 source catalyzed by palladium nanoparticles grafted onto amino-functionalized nanostarch ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Subodh Kumar , Sanny Verma , Suman L. Jain Highly dispersed Pd-nanoparticles grafted onto amino-functionalized nanostarch were found to be excellent heterogeneous catalysts for the direct formylation of various aromatic iodides to their corresponding aldehydes in excellent yields without using any base. The developed catalyst could easily be recovered and recycled for several runs without any significant loss in activity and importantly, no metal leaching was occurred during the reaction. Graphical abstract image
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Microwave-assisted synthesis of coumarin-3-carboxylic acids under ytterbium triflate catalysis ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Serena Fiorito , Salvatore Genovese , Vito Alessandro Taddeo , Francesco Epifano Coumarin-3-carboxylic acids represent a class of natural occurring and semi-synthetic products with valuable reported pharmacological activities. In this Letter a new and improved method for the chemical synthesis of the title compounds is described. Coumarin-3-carboxylic acids have been synthesized in good to excellent yields under microwave irradiation and solvent-free conditions from differently substituted 2-hydroxybenzaldehydes or 2 hydroxyacetophenones and Meldrum’s acid as starting materials in the presence of Yb(OTf)3 hydrate 5% mol as the catalyst. Graphical abstract image
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Mechanism study of the thiol-addition reaction to benzothiazole derivative for sensing endogenous thiols ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Olimpo García-Beltrán , José G. Santos , Sandra Fuentealba , Pedro De la Torre , Paulina Pavez , Natalia Mena , Marco T. Nuñez , Margarita E. Aliaga We kinetically studied the reaction between endogenous thiols such as -γ-glutamylcysteine (γ-Glu-Cys), cysteine (Cys), glutathione (GSH), homocysteine (Hcy), cysteinylglycine (Cys-Gly), and dihydrolipoic acid (DHLA)- with (E)-2-(benzo[d]thiazol-2-yl)-3-(4-morpholinophenyl)acrylonitrile (JGB). Studies conducted by NMR and ESI-MS/MS have demonstrated that this reaction occurs via thiol-addition toward the double bond present in JGB. Considering the product analysis and the pH-dependence of the second order rate constant (k N), we proposed a mechanism that involves the rapid protonation of JGB giving place to an intermediate following by the thiolate attack yielding a final product. Moreover, this probe could successfully sense thiols in the human neuroblastoma SH-SY5Y cells. Graphical abstract image
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β-Cyclodextrin as a supramolecular catalyst for the synthesis of dihydropyrano[2,3-c]pyrazole and spiro[indoline-3,4′-pyrano[2,3-c]pyrazole] in aqueous medium ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Yogesh A. Tayade , Swapnil A. Padvi , Yogesh B. Wagh , Dipak S. Dalal Supramolecular β-cyclodextrin (β-CD) as a highly efficient, biodegradable, and reusable catalyst for the synthesis of pyranopyrazole derivatives is investigated via a one-pot four component reaction of aldehydes and isatins, hydrazine hydrate, malononitrile, and β-keto ester in H2O–EtOH (9:1) at 80°C for first time under neutral conditions. Graphical abstract image
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A rapid route for the preparation of pyrimido[5,4-d]- and pyrido[3,2-d]oxazoles ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Lucas Lemaire , Natascha Leleu-Chavain , Aurélien Tourteau , Alaa Abdul-Sada , John Spencer , Régis Millet Starting from a 5-amino-2-phenyloxazole-4-carbonitrile building block 3, obtained by reaction of benzoyl chloride (1) and aminomalononitrile p-toluenesulfonate (2), a large range of molecules were synthesized in one or two steps. A total of seven pyrimido[5,4-d]oxazoles 5(a–d)–8 and four pyrido[3,2-d]oxazoles 9–12 have been synthesized. Moreover, synthetic procedures have been adapted to overcome the instability of the oxazole ring. Graphical abstract image
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An efficient click-multicomponent strategy for the diversity oriented synthesis of 15–18 membered macrocyclic peptidomimetic fluorophores ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): P. Jithin Raj , D. Bahulayan A general methodology for the three step synthesis of macrocyclic peptidomimetic fluorophores with a range of ring size from 15 to 18 is described. The alternate Mannich type reaction between the halogen functionalized long chain alkyl nitriles with aldehydes and ketones in which one of them decorated with an alkyne functionality leads to the key precursor for the intramolecular copper catalyzed [3+2] azide-alkyne cycloaddition to make the macrocycles obeying Lipinski’s rule of five. Graphical abstract image
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Solid phase synthesis of constrained 13-membered peptide macrocycles employing Fukuyama–Mitsunobu alkylations ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Lei Wang , Wang-Qing Liu , Noémie Saraux , Michel Vidal , Sylvain Broussy Efficient strategies for the solid phase synthesis of constrained macrocyclic peptides are valuable tools for the generation of potentially biologically active compound libraries. In particular, the use of covalent linkers as hydrogen bond surrogates for the initiation and stabilization of α-helical secondary structures, resulting in the formation of a 13-membered macrocycle, is a validated approach. For these purposes, a straightforward synthetic pathway was developed, employing natural amino acids bearing usual protecting groups and mediated through two Fukuyama–Mitsunobu alkylation reactions on unprotected 1,3-propanediol on solid phase. The linear precursors were obtained in good purity and moderate yields, and the final cyclization step was carried out in solution. Graphical abstract image
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Synthesis and fluorescence properties of phenanthro[9,10-d]imidazole derivative for Ag+ in aqueous media ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Bing Zhao , Yu Xu , Yue Fang , Liyan Wang , Qigang Deng A novel fluorescent chemosensor containing 1H-phenanthro[9,10-d]imidazole moieties linked to double ethylenediamino units was synthesized. It exhibits high sensitivity and selectivity in aqueous media for Ag+ with obvious change in color and 12.55-fold fluorescence quenching. The detection limit was calculated as 1.01×10−7 M by a fluorescence titration experiment. The 1:1 binding stoichiometry of L–Ag+ complex was analyzed by Job’s plot and further confirmed by ESI-MS. Furthermore, the recognition pattern was suggested through the FTIR and 1H NMR spectroscopy. Graphical abstract image
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A simple approach for the syntheses of rutaecarpine and its analogs ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Li-Na Liang , Rui An , Tao Huang , Mei Xu , Xiao-Jiang Hao , Wei-Dong Pan , Sheng Liu A novel synthetic route to rutaecarpine and its analogs was accomplished in three steps. The main strategy in our study was based on an elegant construction of the characteristic C/D rings in targeted molecules from the key cyano intermediates in one-pot. Graphical abstract image
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Convenient synthesis of α,α-(bisallyl and bispropargyl)-substituted amines via aza-Barbier-type reaction ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Tao Guo , Ying-Chao Liu , Bo Li , Hong-Min Liu A convenient and efficient approach for the synthesis of α,α-(bisallyl and bispropargyl)-substituted amines has been developed in good yields via Zn-promoted aza-Barbier-type reactions of N-sulfonyl imidates with various allyl and propargyl reagents. The synthetic utility of this approach was demonstrated by the rapid construction of pyrrolidine derivatives. Graphical abstract image
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Cu(OAc)2·H2O—an efficient catalyst for Huisgen-click reaction in supercritical carbon dioxide ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Weiwei Zhang , Xing He , Baoqi Ren , Yuqin Jiang , Zhiguo Hu An efficient protocol for Huisgen-click reaction catalyzed by Cu(OAc)2·H2O for the synthesis of 1,4-disubstituted triazoles has been developed in supercritical carbon dioxide (scCO2) in the absence of ligand at 36°C. The protocol could afford the corresponding products in excellent yield at very low catalyst loadings (0.01mol%). Graphical abstract image
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An efficient protocol for multicomponent synthesis of functionalized chromeno[4,3-b]pyrrol-4(1H)-one derivatives ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Zhiwei Chen , Xiaofeng Yang , Weike Su A concise and efficient synthetic approach was developed for the synthesis of functionalized chromeno[4,3-b]pyrrol-4(1H)-ones via a one-pot, three-component reaction of 4-aminocoumarin, arylglyoxal monohydrates, and aromatic amines promoted by KHSO4 in toluene under reflux condition. The attractive features of this protocol are operational simplicity, short reaction time, easy purification of products and good to excellent yields. Graphical abstract image
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Reductive homocoupling of benzylic halides in aqueous medium using recyclable alumina-supported nickel nanoparticles ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Sagar Khan , Avishek Ghatak , Sanjay Bhar An economical aqueous protocol for the synthesis of bibenzyls has been developed using easily accessible alumina-supported nickel nanoparticles as a stable recyclable heterogeneous catalyst in the presence of hydrazine hydrate as a co-reductant. Various sensitive moieties like alkoxycarbonyl, methylenedioxy, benzyl, chloro, bromo and nitro were tolerated in the aforesaid method. Besides primary benzylic halides, secondary and tertiary benzylic halides reacted efficiently to furnish the homocoupling products without any elimination. Graphical abstract image
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Brønsted acid-catalyzed phenylselenenylation of internal olefins ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Ping Wu , Fei Huang , Jiang Lou , Quannan Wang , Zhuqing Liu , Zhengkun Yu Brønsted acid p-TsOH·H2O-catalyzed phenylselenenylation of α-oxo ketene dithioacetals was efficiently achieved by using N-phenylselenophthalimide (N-PSP) as the phenylseleno reagent. The resultant selenated ketene dithioacetals reacted with styrene in the presence of the same acid to undergo PhSe group transfer, regioselectively affording Markovnikov-type PhSe-alkylated olefins. Their further transformation with phenylboronic acid, guanidine, and hydrazine offers a promising route to access S,Se-incorporated organic compounds. Graphical abstract image
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Synthesis of the azatricyclic ACD ring system of calyciphylline A-type Daphniphyllum alkaloids via a nonstabilized azomethine ylide generated by desilylation ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Ding Ma , Hang Cheng , Chunmei Huang , Liang Xu An efficient synthetic strategy for the direct and rapid construction of the [6-5-7] ACD azatricyclic ring system of numerous calyciphylline A-type alkaloids has been successfully developed. The synthesis featuring an unprecedented protonic acid promoted intramolecular [3+2] cycloaddition via a nonstabilized azomethine ylide generated by desilylation of N-(trimethylsilyl)methyl iminium salt bearing enolizable hydrogens. Graphical abstract image
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Metal free visible light photoredox activation of PhI(OAc)2 for the conversion of arylboronic acids to phenols ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Abhijit Paul , Debnath Chatterjee , Rajkamal , Tanmoy Halder , Srirupa Banerjee , Somnath Yadav The metal free visible light organo-photoredox activation of diacetoxyiodobenzene, PhI(OAc)2 has been carried out using eosin Y and this has been applied for the transformations of arylboronic acids to phenols. The method requires only 0.5 molar equivalents of PhI(OAc)2 and offers a metal free alternative for the transformation. Graphical abstract image
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One-pot synthesis of 3-hydroxyanthranilate derivatives using furans, bromoalkyne, and secondary amines ()
Publication date: 6 May 2015 Source:Tetrahedron Letters, Volume 56, Issue 19 Author(s): Hiroyuki Shinohara , Motohiro Sonoda , Naoya Hayagane , Shota Kita , Shunsuke Okushima , Shinji Tanimori , Akiya Ogawa A novel and convenient method for synthesizing 3-hydroxyanthranilate derivatives using furans, methyl 3-bromopropiolate, and secondary amines was developed. The synthetic reaction consisted of four steps: the Diels–Alder reaction, a conjugate addition reaction, dehydrobromination, and a ring-opening aromatization reaction. A plausible reaction pathway is described on the basis of the structures of the reaction intermediates. By using this method, sterically hindered 3-hydroxyanthranilate derivatives could be obtained selectively in good yields for four-steps. Graphical abstract image
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