Tetrahedron

Editorial board ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14
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Iron catalyzed CN bond formation ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Sujit K. Ghorai, Vijaya G. Gopalsamuthiram, Anup M. Jawalekar, Rupesh E. Patre, Sitaram Pal Diversely functionalized nitrogen-containing heteroaromatic building blocks, fine chemicals and active pharmaceutical or agrochemical ingredients are conveniently prepared via CN bond formation as the key step. Since beginning of the last decade, there has been a flurry of intense research in forging CN bonds using iron catalysts due to their low cost, high natural abundance and non-toxic nature. The present review offers an overview of CN bond forming reactions involving aryl, allyl, propargyl and unactivated alkyl electrophilic substrates with nitrogen nucleophiles via the regular cross coupling reactions catalyzed by iron. In the miscellaneous section, a set of novel transformations facilitated by iron are included as well. Graphical abstract image
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Preparation of novel pyrrol-2-one derivatives via an effective synthesis of new oxazole scaffold ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): İbrahim Evren Kibriz, Mustafa Saçmaci, Ertan Şahin, İsmail Yildirim A convenient procedure for the preparation of oxazole and pyrrole derivatives is described. 2-Amino-1,3-oxazol-2-ones 3a,b were first synthesized from the cyclocondensation reactions of cyanamide (2) with 4-ethoxycarbonyl-5-aryl-2,3-furandione 1a,b, and then new pyrrol-2-ones 5 were synthesized from the reaction of the compounds 3 with various aromatic amines 4. Graphical abstract image
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Acylphloroglucinol derivatives from the twigs and leaves of Callistemon salignus ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Xu-Jie Qin, Hui Liu, Qian Yu, Huan Yan, Jin-Feng Tang, Lin-Kun An, Afsar Khan, Qi-Run Chen, Xiao-Jiang Hao, Hai-Yang Liu Three new acylphloroglucinol derivatives, callisalignones A–C (1–3), six new meroterpenoids, callisalignenes A–F (4–9), along with 18 known analogues (10–27) were isolated from the twigs and leaves of Callistemon salignus. Their structures and absolute configurations were established by comprehensive spectroscopic evidences (NMR, MS, amd electronic circular dichroism calculations). The absolute configurations of callistenones B (13) and H (14) were determined by comparison of their ECD spectra with that of callisalignone B (2). Callisalignones B and C are new adducts of β-triketone and acylphloroglucinol, whereas callisalignenes A–D are new meroterpenoids of acylphloroglucinol and α-phellandrene with different coupling models via hetero-Diels-Alder reaction, respectively. Myrtucommulone D (15) showed significant antibacterial activity against Staphylococcus aureus and three drug resistant S. aureus strains with MIC values of 1.953 and 0.975 μg/mL, respectively. Isomyrtucommulone B (17) displayed remarkable antibacterial activity against Escherichia coli with an MIC value of 0.122 μg/mL. Cytotoxic assay revealed that isomyrtucommulone B (17) was the most active against HCT116 with an IC50 value of 2.09 ± 0.10 μM. Graphical abstract image
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Utilization of flow chemistry in catalysis: New avenues for the selective synthesis of Bis(indolyl)methanes ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Swapna S. Mohapatra, Zoe E. Wilson, Sujit Roy, Steven V. Ley Flow chemistry enables the preparation of bis(indolyl)methanes from various indoles and structurally divergent aldehydes using Sc(OTf)3 catalysis. The reaction is regioselective for C-3 functionalization of the indoles, occurring over short reaction times allowing for rapid investigation of scope with straightforward work up facilitating product isolation. Graphical abstract image
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Total syntheses of both enantiomers of amphirionin 4: A chemoenzymatic based strategy for functionalized tetrahydrofurans ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Arun K. Ghosh, Prasanth R. Nyalapatla The total syntheses of (−)-amphirionin-4 and (+)-amphirionin-4 have been achieved in a convergent and enantioselective manner. The tetrahydrofuranol cores of amphirionin-4 were constructed in optically active form by enzymatic resolution of racemic cis-3-hydroxy-5-methyldihydrofuran-2(3H)-one. The polyene side chain was efficiently synthesized using Stille coupling. The remote C8-stereocenter was constructed using the Nozaki-Hiyama-Kishi coupling reaction. Detailed 1H NMR studies of Mosher esters of (−)-amphirionin-4 and (+)-amphirionin-4 were carried out to support the assignment of the absolute configurations of the C-4 and C-8 asymmetric centers of amphirionin-4. Graphical abstract image
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Polyaromatic heterocycles through intramolecular alkyne carbonyl metathesis: 5-Acylnaphtho[2,1-b]benzofurans ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Maloy Nayak, Dileep Kumar Singh, Ikyon Kim A modular approach to 5-acylated naphtho[2,1-b]benzofurans was developed where Sonogashira cross-coupling and intramolecular alkyne carbonyl metathesis were sequentially employed to build the aromatic benzene C ring of naphtho[2,1-b]benzofuran with an acyl group at the C5 position. Graphical abstract image
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Protonation-induced switching of pleated foldamers of diaminonaphthalene-bipyridinium polymers ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Lan Chen, Hui Wang, Dan-Wei Zhang, Yaming Zhou, Zhan-Ting Li 1,5-diaminonaphthalene (DAN) and bipyridinium (BIPY2+) were copolymerized into NP1 and NP2 linked by acylhydrazone bonds. The formed intramolecular charge-transfer (CT) complex drove the linear foldamers to adopt pleated folding conformation. Upon protonation of the DAN units by triflic acid (TFSA), the pleated folding conformation unfolded to linear structure because of electron repulsion. And this linear structure can be refolded to pleated structure by titrating with triethylamine (TEA). 1,5-dinaphtho[38]crown-10 (DN38C10) can encapsulate bipyridinium group on the polymers after protonation. These processes were supported by UV–vis and fluorescence spectroscopy studies. Graphical abstract image
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Solvent- and temperature-controlled inversion of π-facial selectivity in the 1,2-cycloaddition of singlet oxygen to hydroxyphenyl-substituted cyclohexadihydrofurans ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Nobuko Watanabe, Kiriko Hiragaki, Kunihiko Tsurumi, Hisako K. Ijuin, Masakatsu Matsumoto Singlet-oxygenation of 3-hydroxyphenyl-substituted dihydrofurans fused with a cyclohexane 1a−c exclusively gave the corresponding syn/anti-stereoisomeric mixtures of dioxetanes 2a−c. The syn/anti-π-facial selectivity in the 1,2-cycloaddition of singlet oxygen (1O2) was found to be remarkably sensitive to the solvent as well as the reaction temperature. In fact, the solvent effect was so conspicuous that inversion of the syn/anti-π-facial selectivity was observed in different solvents, such as chloroform and toluene. An LSER (linear solvation energy relationships) analysis suggested that the Lewis-acidity/basicity and HBD (hydrogen-bond donor)/HBA (hydrogen-bond acceptor) ability as well as dipolarity/polarizability of the solvent played an important role in this change in syn/anti-π-facial selectivity. An investigation of the temperature-dependency of the singlet-oxygenation suggested that the syn/anti-π-facial-selective 1,2-cycloaddition of 1O2 to 1 was a conformationally-(entropy-) controlled process. Graphical abstract image
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Metal-free visible-light-promoted intermolecular [2+2]-cycloaddition of 3-ylideneoxindoles ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Ling-Ling Wu, Gao H. Yang, Zhi Guan, Yan-Hong He The Rose Bengal sensitized intermolecular [2 + 2]-cycloaddition of 3-ylideneoxindoles for the synthesis of spirocyclic oxindoles was developed successfully under visible light irradiation conditions. The cycloaddition products were obtained in good yields (up to 93%) with excellent diastereoselectivity and regioselectivity by using a low loading of Rose Bengal (0.125 mol%) as a triplet sensitizer. This work demonstrates the potential benefits of Rose Bengal in visible light catalysis. Graphical abstract image
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Formation of 3-[amino(aryl)-methylidene]-1,3-dihydro-2H-indol-2-ones involving ring transformation of 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Richard Kammel, Denisa Tarabová, Břetislav Brož, Veronika Hladíková, Jiří Hanusek The reaction of 3-bromooxindole with substituted (hetero)aromatic thioamides in acetonitrile was studied. At room temperature the reaction preferably gives products of ring transformation i.e. 2-aryl-5-(2-aminophenyl)-4-hydroxy-1,3-thiazoles (3b-f,h) whereas at elevated temperature products of an Eschenmoser coupling reaction, i.e. 3-[amino(aryl)-methylidene]-1,3-dihydro-2H-indol-2-ones (2b-f), are formed exclusively. There exist only two exceptions (4-methoxy and 2-pyridinthioamide) in which the Eschenmoser coupling reaction always takes place giving 2a and 2g. Also N-methylation of the starting 3-bromooxindole completely prevents formation of thiazoles. The prepared thiazoles 3b-f are unstable in solution and they undergo slow ring transformation to 2b-f. The rate limiting step of this rearrangement involves cleavage of an intermediary thiirane ring, which is slowed down by electron-withdrawing substituents on the thioamide (ρ = −1.15). Graphical abstract image
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One-pot synthesis of 1,3,4-thiadiazoles using Vilsmeier reagent as a versatile cyclodehydration agent ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Maaroof Zarei A simple and efficient synthetic method for the one-pot synthesis of 1,3,4-thiadiazoles utilizing Vilsmeier reagent was developed. In this method carboxylic acids and hydrazine were converted to 1,3,4-thiadiazoles in the presence of Vilsmeier reagent and Lawesson's reagent. The influence of the thionation reagent, solvent, temperature and time, in this reaction was discussed. The developed methodology for 1,3,4-thiadiazole synthesis has the advantage of simplicity, ambient reaction conditions, easy purification and good to excellent yield of products. Graphical abstract image
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Lipase-mediated regioselective modifications of macrolactonic sophorolipids ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Aliya Sembayeva, Beniam Berhane, Jason A. Carr Chemoenzymatic synthesis and modification of well-defined macrolactonic sophorolipid (SLML) analogues via a series of successive regioselective de-esterification/transesterification reactions is investigated. Of the lipases screened, Candida antartica lipase- B (Novozyme-435) successfully deacylated the C-6′ acetoxy group of natural and peracylated SLMLs. Subsequent transesterification with acylating agents (esters of fatty acids) was successful only with the C-6′ deacetylated natural SLML providing an avenue to well-defined analogues of varying amphilicity. The macrolactonic motif was essential for enzymatic recognition of the sophorose rings of these complex glycolipids. In the absence of the lactonic motif, the peracylated sophorose rings are not deacylated, rather the carboxyl end of the non-lactonic forms that was preferentially transesterified. All macrolactonic derivatives were characterized by IR, 1H, 13C, 1H-1H and 1H-13C NMR spectroscopy, as well as HRMS where applicable. Graphical abstract image
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Synthesis of N-benzyl-des-D-ring lamellarin K via an acyl-Claisen/Paal-Knorr approach ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Nora Dittrich, Lisa I. Pilkington, Euphemia Leung, David Barker Lamellarin K is a complex pyrrole natural product and member of the lamellarin family – a group of natural products known for their potent biological activities, such as, antiproliferative activity and inhibition of P-gp mediated drug efflux pumps. We herein describe the synthesis of the N-benzyl-des-D ring analogue of lamellarin K using a route that centres on an acyl-Claisen reaction to eventually prepare a highly-functionalised 1-aryl-4-methyl-1,4-diketone. Paal-Knorr pyrrole formation using this diketone undergoes auto-oxidation to give a fully-substituted 5-formyl pyrrole which was converted into the natural lactone B ring. Antiproliferative testing of the N-benzyl-des-D ring analogue gave an IC50 of 2.63 μM against the MDA-MB-231 breast cancer cell line. Graphical abstract image
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An efficient, scalable approach to hydrolyze flavonoid glucuronides via activation of glycoside bond ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Xue-Yang Jiang, Xin-Chen Li, Wen-Yuan Liu, Yun-Hui Xu, Feng Feng, Wei Qu Hydrolyzing flavonoid glucuronides into corresponding aglycones posed some significant challenges. To improve acid-catalyzed hydrolysis process of flavonoid glucuronide, structures of glucuronide, hydrolysis parameters and post-processing were optimized. The optimized condition was performed by hydrolysis flavonoid glycoside methyl ester in a mixed solvent consisting of 2 mol/L H2SO4/EtOH/H2O (1/8/1, v/v/v) at 95 °C for 7 h and resulted in up to 90% aglycone yields, minimal byproduct formations and milder hydrolysis conditions. Furthermore, the optimized method avoids tedious purification steps and is easily conducted on a relatively large-scale using economical and commercially available reagents. Graphical abstract image
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Palladium(II)-catalyzed aerobic intramolecular allylic CH activation for the synthesis of indolines ()
Publication date: 6 April 2017 Source:Tetrahedron, Volume 73, Issue 14 Author(s): Changrui Xu, Zhengxing Wu, Jianzhong Chen, Fang Xie, Wanbin Zhang A method for the preparation of indolines via palladium-catalyzed aerobic intramolecular allylic CH activation was developed. Oxygen was successfully used as oxidant with catalytic amount of 1,4-benzoquinone. 16 examples were reported, the majority of substrates gave moderate to good yields. Graphical abstract image
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Editorial board ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13
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Synthesis and anti-parasitic activity of C-benzylated (N-arylcarbamoyl)alkylphosphonate esters ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Christiana M. Adeyemi, Michelle Isaacs, Dumisani Mnkandhla, Rosalyn Klein, Heinrich C. Hoppe, Rui W.M. Krause, Kevin A. Lobb, Perry T. Kaye Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl)phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle. Graphical abstract image
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Palladium-catalyzed direct arylation of maleimides: A simple route to bisaryl-substituted maleimides ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Farnaz Jafarpour, Mitra Shamsianpour, Salumeh Issazadeh, Masoumeh Dorrani, Hamideh Hazrati Palladium-catalyzed direct arylation of maleimides via Heck as well as organoboron-mediated Heck-type reactions are developed. These methods offer an approach to a wide variety of biologically interesting 3,4-diarylmaleimide scaffolds from readily accessible starting materials. These approaches led to the feasible one-pot construction of bisaryl-substituted maleimides which have historically been problematic. Graphical abstract image
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Theoretical exploration of mechanism of carbapenam formation in catalytic Kinugasa reaction ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Mahdieh Darroudi, Yaghoub Sarrafi, Mahshid Hamzehloueian Molecular mechanism of catalytic Kinugasa reaction of a cyclic nitrone and acetylene, derived from d-glyceraldehyde acetonide, using acetonitrile as a ligand and solvent is studied with density functional theory methods. Possible pathways of Cu(L) catalyzed 1,3-diploar cycloaddition/rearrangement cascade reaction are investigated. For a cycloaddition process, two possible mechanisms have been characterized: the first one corresponds to a one-step cycloaddition with a high activation barrier. The second one corresponds to the mono- or di-copper catalyzed stepwise process that in terms of calculated energy barriers, di-copper path is the most favorable. The reaction proceeds by rearrangement with two competitive mechanisms, formation of bicyclic oxaziridinium intermediate or ketene intermediate. Our calculations show that formation of ketene intermediate is the lowest energy pathway for the rearrangement process. Graphical abstract image
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Structural and stereochemical elucidation of new hygrophorones from Hygrophorus abieticola (Basidiomycetes) ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Alexander Otto, Andrea Porzel, Bernhard Westermann, Wolfgang Brandt, Ludger Wessjohann, Norbert Arnold Four new hygrophorones (1–4) together with the known hygrophorone B12 (5) have been isolated from fruiting bodies of the basidiomycete Hygrophorus abieticola Krieglst. ex Gröger & Bresinsky. Their structures were assigned on the basis of extensive one and two dimensional NMR spectroscopic analyses as well as ESI-HRMS measurements. Among these compounds, two previously undescribed hygrophorone types, named hygrophorone H12 (3) and 2,3-dihydrohygrophorone H12 (4), were identified. The absolute configuration of hygrophorone E12 (2) is suggested based on quantum chemical CD calculations, while a semisynthetic approach in conjunction with computational studies and analysis of NOE interactions allowed the stereochemical assignment of compounds 3 and 4. Additionally, semisynthetic derivatives of hygrophorone B12 (5) were generated by acetylation of the hydroxyl groups. The biological activity of the natural and semisynthetic hygrophorones was evaluated against phytopathogenic organisms, revealing that the α,β-unsaturated carbonyl functionality is likely to be an essential structural feature. Hygrophorone B12 (5) was identified as the most active compound, acting against both ascomycetous fungi and oomycetes. Graphical abstract image
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Solvent-dependent selective fluorescence sensor for Zn2+ and Al3+ based on a new diarylethene with a salicylal schiff base group ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Lele Ma, Gang Liu, Shouzhi Pu, Chunhong Zheng, Congbin Fan A novel photochromic diarylethene with a salicylidene Schiff base group was synthesized and its multi-controllable fluorescence switching properties induced by light, base, and metal ions were investigated. The diarylethene displayed sequence-dependent responses through efficient interaction of the salicylidene Schiff base group with base and metal ions, and it could serve as a naked-eye chemosensor for highly selective detection of different metal ions in different solvents. When triggered by Zn2+ in acetonitrile, its fluorescence was enhanced by 400 fold with a concomitant color change from dark to bright yellow. In contrast, when it bound to Al3+ in methanol, its fluorescence was enhanced by 110-fold accompanied with a color change from dark to bright cyan. On the basis of its light-, base-, and metal-responsive fluorescence behaviors, two complicated logic gates were constructed using the fluorescence intensity as output and combinational stimuli of light and chemical species as inputs. Graphical abstract image
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Exploratory spectroscopic and computational studies of the anion binding properties of methyl hyocholate in organic solvent ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Giancarlo Fantin, Marco Fogagnolo, Ignacio Delso, Pedro Merino The binding properties of methyl hyocholate 1a toward F−, Cl−, Br− and CH3CO2 − anions were explored by 1H and 13C NMR, ESI-MS measurements and computational calculations. The 1H NMR titration suggested that 1a forms a 1:1 complex with the selected anions. These complexes have also been detected by ESI-MS measurement even though the MS spectra showed that the stoichiometry of the predominant host-guest species in the gas phase is 2:1. 13C NMR and computational data suggested that the hydroxyl groups at C6 and C7 positions are more involved than the hydroxyl group at C3 position in the binding of spherical F−, Cl−, Br− anions while in the case of the Y-shaped acetate ion two different conformers (in equilibrium) are present: the first showing interaction with both the two hydroxyl groups at C6 and C7 positions, the second also involving the participation of the third hydroxyl group at C3 position. Graphical abstract image
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Copper-catalyzed hydrophosphinylation of terminal ynamides with H-phosphinates ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Atsushi Kinbara, Makoto Sato, Kana Yumita, Takehiro Yamagishi A method for Cu(OAc)2-catalyzed hydrophosphinylation of ynamides was developed and applied to several types of terminal ynamides and H-phosphinates. The products were transformed into β-aminophosphinates, which are useful for the preparation of biologically active compounds. Graphical abstract image
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Study on the cycloaddition reactions of pyrrolotriazepine derivatives with nitrile oxides. Synthesis of new fused tricyclic ring systems ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Tamás Földesi, András Dancsó, Balázs Volk, Mátyás Milen Representatives of new tricyclic ring systems based upon the pyrrolotriazepine core, have been synthesized at our laboratory using cycloaddition reactions of 1-aryl-pyrrolotriazepinones or 1,4-diarylpyrrolotriazepines in a dichloromethane solution at room temperature, with nitrile oxides generated in situ from N-hydroxyarylcarboximidoyl chlorides with triethylamine. The reaction between 1-aryl-3H-pyrrolo[2,1-d][1,2,5]triazepin-4(5H)-ones and the corresponding nitrile oxides led to 3,11b-diaryl-5H,11bH-[1,2,4]oxadiazolo[4,5-b]pyrrolo[2,1-d][1,2,5]triazepin-6(7H)-one derivatives. Cycloaddition reactions of 1,4-diaryl-5H-pyrrolo[2,1-d][1,2,5]triazepines under similar conditions gave two products, depending on which double bond was involved in the cycloaddition: 3,6,11b-triaryl-7H,11bH-[1,2,4]oxadiazolo[4,5-b]pyrrolo[2,1-d][1,2,5]triazepines and 3,6,11a-triaryl-11,11a-dihydro[1,2,4]oxadiazolo[4,5-b]pyrrolo[1,2-e][1,2,5]triazepines. The structures of the new compounds were also justified by 2D NMR and single-crystal X-ray measurements. Graphical abstract image
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How does the global electron density transfer diminish activation energies in polar cycloaddition reactions? A Molecular Electron Density Theory study ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Luis R. Domingo, Mar Ríos-Gutiérrez, Patricia Pérez The key role of the Global Electron Density Transfer (GEDT) in polar cycloaddition reactions is analysed within the Molecular Electron Density Theory (MEDT) using Density Functional Theory (DFT) calculations at the MPWB1K/6-311G(d) computational level. A comparative MEDT study of the non-polar Diels-Alder reaction between cyclopentadiene (Cp) and ethylene and the polar Diels-Alder reaction between Cp and tetracyanoethylene makes it possible to establish that the GEDT taking place in the direction of the transition state structures favours the bonding changes required for the formation of the new CC single bonds along polar cycloaddition reactions. Analysis of the reactivity indices defined within the conceptual DFT at the ground state of the reagents makes it possible to predict the reactivity of organic molecules in polar reactions. Graphical abstract image
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Installation of α-ketocarboxylate groups to C7-position of indolines via C−H addition and oxidation approach under ruthenium catalysis ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Hyeim Jo, Jihye Park, Neeraj Kumar Mishra, Mijin Jeon, Satyasheel Sharma, Hyunjung Oh, Seok-Yong Lee, Young Hoon Jung, In Su Kim The ruthenium(II)-catalyzed site-selective acylation of indolinic C−H bonds with ethyl glyoxalate is described. A cationic ruthenium catalyst in the presence of copper(II) acetate was found to be an optimal catalytic system for the construction of C7-indolinyl ketoesters. In this process, C−H addition reaction first takes place, and subsequent oxidation of alcohol intermediates occur in-situ. The formed C7−functionalized indolines can be a crucial array towards the construction of novel bioactive molecules. Graphical abstract image
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Synthesis and stereochemistry of decarestrictines H and J ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Ryo Katsuta, Naoko Masada, Yuichiro Shimodaira, Saeko Ueda, Arata Yajima, Tomoo Nukada The first synthesis of (7S,9R)-decarestrictine H and (7R,9R)-decarestrictine H as well as the improved synthesis of decarestrictine J were achieved. The overall yields of (7S,9R)-decarestrictines H and J were 20.9% each in nine to ten steps from (R)-Roche ester using a unified synthetic route via esterification with 3,3-ethylenedioxyhex-5-enoic acid and ring-closing metathesis, which were the key steps. The relative stereochemistry of decarestrictine H was determined to be 7,9-syn by comparing the spectral data of the natural product and synthetic epimers of decarestrictines H. Graphical abstract image
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Sugar migration induced by the Wagner-Meerwein rearrangement of 28-O-glycosyl-betulin derivatives ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Anna Korda, Zbigniew Pakulski, Piotr Cmoch, Katarzyna Gwardiak, Romuald Karczewski Treatment of betulin-type saponins, in which the sugar moiety is connected at the 28-position, with TMSOTf affords 3-O-substituted allobetulin saponins. This unprecedented migration of the sugar part is driven by the Wagner-Meerwein rearrangement of the betulin core. According to our mechanistic studies an oxocarbenium ion released during the rearrangement reacts with the free 3-OH group of the triterpene affording the final allobetulin saponin. Migration rate depends on the size and configuration of the sugar moiety. Graphical abstract image
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Synthesis and anti-bacterial activity of a library of 1,2-benzisothiazol-3(2H)-one (BIT) derivatives amenable of crosslinking to polysaccharides ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Fiorenza Viani, Bianca Rossi, Walter Panzeri, Luca Merlini, Alessandra M. Martorana, Alessandra Polissi, Yves M. Galante 1,2-Benzisothiazol-3(2H)-one (BIT) is one of the most common chemical biocides in industrial products, with a heterocyclic structure and a wide range of antimicrobial activity. A library of BIT derivatives was synthesized and characterized, from which 18 compounds were selected, tested for anti-bacterial activity relative to the parent molecule and amenable of coupling to plant polysaccharides in general and to galactomannans (GM) in particular, widely used as rheology modifiers, but with limited “biostability”. Four sites on the BIT core were targeted: the nitrogen and the oxygen atoms on the heterocyclic ring, the C5 and the C6 positions on the aromatic ring, where functional groups were introduced. The ultimate aim of this work is to establish whether by covalently linking a biocide to GM polymers, their “biostability” can be improved. Graphical abstract image
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Fe(OTf)3-catalyzed tandem Meyer-Schuster rearrangement/intermolecular hydroamination of 3-aryl propargyl alcohols for the synthesis of acyclic β-Aminoketones ()
Publication date: 30 March 2017 Source:Tetrahedron, Volume 73, Issue 13 Author(s): Ruiheng Tao, Yan Yin, Yongbin Duan, Yuxing Sun, Yue Sun, Fengkai Cheng, Jinpeng Pan, Cheng Lu, Yuan Wang Fe(OTf)3-catalyzed synthesis of acyclic β-aminoketones from 3-aryl propargyl alcohols and nitrogen nucleophiles were investigated. Results showed that propargyl alcohols without bulky groups α to the hydroxyl group underwent the transformation smoothly. Sulphonamides exhibited the higher reactivity than amides as the nitrogen nucleophiles and the transformation of acyclic β-aminoketones were finished in shorter reaction time and higher yields. Finally, racemic fluoxetine was efficiently accessed with the present reaction as the first step. This novel synthesis of acyclic β-aminoketones probable proceeded a Fe(OTf)3-catalyzed Meyer-Schuster rearrangement of 3-aryl propargyl alcohols, followed by a intermolecular hydroamination between nitrogen nucleophiles and α, β-unsaturated ketones. Graphical abstract image
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Editorial board ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12
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CO2 capture capacity of five- and six-membered cyclic amidines bearing silatranyl group under dry conditions ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Naoto Aoyagi, Takeshi Endo CO2 capture and release behaviors of three amidines bearing silatranyl group in DMSO solution were evaluated under dry conditions containing a very small amount of water. A six-membered cyclic amidine with silatranyl group captured CO2 at 25 °C under atmospheric pressure quantitatively, and the trapped CO2 was released at 60 °C under Ar atmosphere. A five-membered cyclic amidine with silatranyl group also captured CO2, but less efficiently, under the same conditions as above. In contrast, an acyclic amidine with silatranyl group did not capture CO2 at all, as expected from the poor CO2-capturing ability of the acyclic amidine moiety. Graphical abstract image
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Critical role of select peptides in the loop region of G-rich PNA in the preferred G-quadruplex topology and stability ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Tanaya Bose, Vaijayanti A. Kumar An uncharged PNA 15mer sequence formed unimolecular antiparallel G-quadruplex similar to that observed for DNA-TBA. Replacement of ‘tt’ loop regions by peptides which induce helices or turns were found to have unpresidented effect on the quadruplex topology and stability. This study opens up a completely new strategy of utilizing G-quadruplex formation to display the array of functional groups in the three dimensional space thus creating a possibility of getting closer to the dream of designed peptides with three dimensional structures as observed in catalytic protein folds. Graphical abstract image
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Cationic Pd(II)-catalyzed arylative cyclization of N-(2-formylaryl)alkynamides: An efficient route to 2-quinolinones ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Xiaojuan Zhang, Xiuling Han, Junjie Chen, Xiyan Lu A cationic palladium complex catalyzed arylative cyclization reaction of N-(2-formylaryl)alkynamides with arylboronic acids was developed. This new process provides an efficient way for the synthesis of functionalized 2-quinolinones in good to excellent yields under mild conditions. Some control experiments were conducted to explain the possible mechanism for the formation of the products. Graphical abstract image
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Assessing stereoelectronic effects in dipolar cycloadditions yielding fused thiazolopyridone rings ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Juan García de la Concepción, Martín Ávalos, Reyes Babiano, Pedro Cintas, José L. Jiménez, Mark E. Light, Juan C. Palacios We report a combined experimental and computational study on the cycloadditions of bicyclic 1,3-thiazolium-4-olates, derived from thiazolidin-2-thiones, with asymmetrically-substituted acetylenes. These results provide further mechanistic insights into the above dipolar cycloadditions and enable an unequivocal characterization by NMR spectroscopy of regiochemical patterns as previous derivatives had substituents at both C-2 (in the dipole) and C-6 (in products). Accordingly, new dihydrothiazolopyrid-2-ones have been obtained from a thioisomünchnone lacking substitution at C-2. With the aim of assessing the steric hindrance as well as the facial stereoselection induced by a bulky group on the Si face (relative to C-7a) of the mesoionic heterocycle, a chiral thioisomünchnone has also been obtained along with the resulting optically active thiazolopyridones. A computational study of these particular cycloadditions, largely based on an NBO analysis, allowed us to evaluate the influence of substituents on intermolecular steric repulsions, charge transfers, as well as solvent effects. Graphical abstract image
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Lanostane triterpenoids from the edible mushroom Astraeus asiaticus ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Masahiko Isaka, Somporn Palasarn, Sujinda Sommai, Sukitaya Veeranondha, Kitlada Srichomthong, Palangpon Kongsaeree, Samran Prabpai Seven new lanostane triterpenoids, astraeusins M–Q (1–5), 26-epi-artabotryol C1 (6), and 26-epi-astrasiaone (7), together with seventeen known compounds (8–24), were isolated from the food mushroom Astraeus asiaticus. The C-26 configuration of artabotriol C1 and astrasiaone, originally reported as 26R (6 and 7, respectively), was revised to be 26S (16 and 17, respectively). Astraeusin M (1) exhibited antimalarial activity against Plasmodium falciparum K1 with an IC50 value of 3.0 μg/mL. Graphical abstract image
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Diastereoselective synthesis of D-threo-sphinganine, L-erythro-sphinganine and (−)-spisulosine through asymmetric α-hydroxylation of a higher homologue of Garner's aldehyde ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Vipin Kumar Jain, Ramesh Ramapanicker A diastereoselective route to the synthesis of D-threo-sphinganine, L-erythro-sphinganine and (−)-spisulosine from the higher homologue of Garner's aldehyde prepared from l-aspartic acid is reported. While the starting material contains one of the stereocenters in the target molecules, the other is generated by proline-catalyzed asymmetric α-hydroxylation of the aldehyde function. The two diastereomers of sphinganine are prepared from the same starting material and using the same sequence of reactions, but for the proline isomer used as the catalyst. The method described is simple and efficient and can easily be extended for the synthesis of other sphingoid bases. Graphical abstract image
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Ortho lithiation-in situ borylation of substituted morpholine benzamides ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Anna Cederbalk, Morten Lysén, Jan Kehler, Jesper L. Kristensen Morpholine amides are cheap and safe alternative to Weinreb amides as acylating agents of organometallic species. Herein, the in-situ lithiation/borylation of 18 ortho- meta- and para-substituted morpholine benzamides has been investigated. 10 of the 18 substrates provided the desired boronic esters as the major isomer (>90% regioselectivity) in crude isolated yields ranging from 68 to 93%. The synthetic usability of such building blocks was subsequently illustrated via the synthesis of a kinase inhibitor. Graphical abstract image
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Reaction of 3-chloroquinoline-2,4-diones with ethanolamine and rearrangement of the reaction products ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Antonín Klásek, Filip Křemen, Hana Křemenová, Antonín Lyčka, Michal Rouchal The reaction of tertiary α-chloroketones with ethanolamine has not been hitherto described in the literature. Herein, we describe the reaction of tertiary 3-chloroquinoline-2,4-diones with ethanolamine to give novel 3-(2-hydroxyethylamino)quinoline-2,4-diones. These compounds provide 3-(2-oxooxazolidin-3-yl)quinoline-2,4(1H,3H)-diones and new compounds with dimeric character after reaction with triphosgene. Molecular rearrangement proceeds during the reaction of 3-(2-hydroxyethylamino)quinoline-2,4-diones with isocyanic acid. Three types of reaction products arise: 2-(2-hydroxyethyl)imidazo[1,5-c]quinazoline-3,5-diones, 3-(2-hydroxyethyl)-3,3a-dihydro-2H-imidazo[4,5-]quinoline-4(5H)diones and primarily 5-hydroxy-1-(hydroxyethyl)-1′H-spiro[imidazolidine-5,3′-indole]-2,2′-diones. The reaction mechanism and product stereochemistry are discussed. The 1H, 13C and 15N NMR spectra of the prepared compounds were measured, and all resonances were assigned from appropriate two-dimensional experiments. Graphical abstract image
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Terpenoids with potent antimycobacterial activity against Mycobacterium tuberculosis from Trigonostemon reidioides roots ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Praphakorn Kaemchantuek, Ratchanaporn Chokchaisiri, Samran Prabpai, Palangpon Kongsaeree, Warangkana Chunglok, Tanyarath Utaipan, Walee Chamulitrat, Apichart Suksamrarn Phytochemical investigation of Trigonostemon reidioides roots led to the isolation of fourteen compounds. These included six new diterpenoids, trigonoreidons A−F (1−6), together with eight known diterpenoids 7−14. The structures of the new compounds were elucidated by spectroscopic techniques and the absolute configuration at the asymmetric carbon was determined by the modified Mosher's method. The structure of trigonoreidon B (2) was confirmed by X-ray crystallographic analysis. The known compounds were identified by comparison of the spectroscopic and physical data with those of reported values. The isolated compounds were evaluated for antimycobacterial activity against Mycobacterium tuberculosis. Among the compounds that exhibited antimycobacterial activity, the diterpenoids rediocide C (12) and rediocide G (14) were the most active compounds, with the MIC value of 3.84 μM. Graphical abstract image
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The AIEE properties and solid state fluorescence of 3-indolyl-4-indazolyl maleimide compounds: Synthesis and fluorescence characteristics ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Bo-ye Zhu, Liang Han, Yu-Jin Li, Jian-rong Gao, Qing Ye A range of 3-indolyl-4-indazolyl maleimide fluorescent compounds, including 2a, 2b, 2c, 3a and 3b, were synthesized efficiently. In different organic dissolvents, the photo-physical performance was checked, either in the aggregated state or in the solid state. When being in solid and in solution state, these fluorescent compounds showed high fluorescent intensity, indicating a highest fluorescence quantum efficiency of 45% accompanying a large Stokes Shift longer than 100 nm in toluene. Also, they can carry out a phenomenon of aggregation-induced emission enhancement (AIEE). TDDFT and DFT calculations were used to confirm the experimental findings. Graphical abstract image
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New biphenantherene and nervogenic acid derivatives from Liparis regnieri Finet and their inhibitory activities against NF-κB activation ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Jie Ren, Chao Fan, Yi-Gong Guo, Shi-Kai Yan, Richard D. Ye, Yan Zhang, Hui-Zi Jin, Wei-Dong Zhang A phytochemical investigation of the whole plant of Liparis regnieri Finet led to the isolation of one new biphenantherene (1) and ten new nervogenic acid derivatives (2–11), together with nine known compounds. Their structures were elucidated mainly by extensive analyses of 1D and 2D NMR spectroscopic data and chemical reactions. Additionally, for the first time a previously unreported biphenantherene was discovered to effectively suppress TNF-α induced expression of NF-κB-Luc in Hela cells with the IC50 value of 1.80 μM and the structure-activity relationshipwas also discussed. Graphical abstract image
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Bromination of quinoxaline and derivatives: Effective synthesis of some new brominated quinoxalines ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Sefa Uçar, Selçuk Eşsiz, Arif Daştan The synthesis of brominated quinoxaline derivatives starting from several kinds of quinoxaline by different bromination strategies was studied. First the synthesis of some brominated quinoxalines was accomplished along with the development of an alternative and effective synthesis of some known compounds. A new, clean, and effective synthetic method for selective reduction of quinoxaline to 1,2,3,4-tetrahydroquinoxaline was also developed. The products obtained were characterized by means of NMR spectroscopy, elemental analyses, and mass spectrometry. Graphical abstract image
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Development of an unexpected reaction pathway for the synthesis of 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines through palladium-catalyzed cascade reactions ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Ali Keivanloo, Atena Soozani, Mohammad Bakherad, Mahdi Mirzaee, Hadi Amiri Rudbari, Giuseppe Bruno 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines are synthesized through the multi-component reaction of 3-substituted 2-chloroquinoxalines, propargyl bromide, and excess secondary amines in the presence of a palladium copper catalytic system. This one-pot process provides an unexpected synthesis of new trisubstituted pyrrolo[1,2-a]quinoxalines by the introduction of two amine substituents onto the fused pyrrole rings in a single reaction procedure. The compounds formed are fully characterized by the analytical spectral data and X-ray analysis. A number of synthesized pyrrolo[1,2-a]quinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, Pseudomonas aeruginos, and Bacillus subtilis. According to the results obtained, compounds 3b, 3c, and 3e are active against M. luteus, compounds 3b and 3e are active against Ps. Aeruginos, and only compound 3f is active against all the three bacterial strains. Graphical abstract image
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Unexpected regioselectivity observed in the bromination and epoxidation reactions of p-benzoquinone-fused norbornadiene: An experimental and computational study ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Selcuk Essiz, Erdin Dalkilic, Ozlem Sari, Arif Dastan, Metin Balci The bromination reaction of p-benzoquinone-fused norbornadiene was studied at various temperatures (−78, −50, 0, 25, and 77 °C). At room temperature, the double bonds of the p-benzoquinone units were mainly brominated. The double bond of the norbornene unit also underwent a bromination reaction in a yield of only 2%. However, the reaction at −78 °C resulted in the formation of products derived from the attack of bromine on the norbornene double bond with higher charge density. In contrast to the bromination reaction, the epoxidation reaction of the same compound with m-chloroperbenzoic acid and dimethyldioxirane exclusively resulted in the formation of products derived from the addition to the double bond of norbornadiene. The regioselectivity observed was investigated and the results were supported by theoretical calculations. Graphical abstract image
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Mesogenic heterocyclic pyrazoles, isoxazoles and 1,3,4-oxadiazoles ()
Publication date: 23 March 2017 Source:Tetrahedron, Volume 73, Issue 12 Author(s): Zih-Yang Lei, Hsiu-Ming Kuo, Chung K. Lai Three new series of liquid crystals 1-3 derived from heterocyclic pyrazoles, isoxazoles and 1,3,4-oxadiazoles exhibiting smectic A or C phases were reported. Compound 1a exhibited monotropic smectic A phase, while the other two compounds 2-3a were not mesogenic. In contrast, all other compounds 1-3b bearing longer alkoxy chains exhibited smectic X and C phases, which were confirmed by powder XRD diffractometer. The clearing temperatures decreased in the order of compounds 1b > 2b > 3b, in contrast the temperature range of smectic C phases increased in the order of compounds 1b < 2b < 3b. The smectic phases in 1-3b were formed by a monomeric structure, confirmed and consistent with powder X-ray diffraction data. The formation of mesomorphic behavior might be probably attributed to their exocyclic angles and/or H-bonds. All derivatives showed good stabilities at temperature below T = 346 °C on TGA analysis. Graphical abstract image
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Editorial board ()
Publication date: 16 March 2017 Source:Tetrahedron, Volume 73, Issue 11
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An efficient stereoselective synthesis of six stereoisomers of 3, 4-diaminocyclohexane carboxamide as key intermediates for the synthesis of factor Xa inhibitors ()
Publication date: 16 March 2017 Source:Tetrahedron, Volume 73, Issue 11 Author(s): Xin Wang, Mingliang Ma, Alavala Gopi Krishna Reddy, Wenhao Hu An efficient stereoselective route for the preparation of six stereoisomers of tert-butyl ((1R, 2S, 5S)-2-amino-5-(dimethylcarbamoyl)cyclohexyl)carbamate 1 starting from simple 3-cyclohexene-1-carboxylic acid has been described. Stereochemistry of the title compounds was controlled at C2 center by Mitsunobu reaction and at C5 via a base-catalyzed epimerization. Only a limited usage of column chromatography has provided a direct and scalable route for the six stereoisomers. Graphical abstract image
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TEMPO-catalyzed oxidative dimerization and cyanation of indoles for the synthesis of 2-(1H-indol-3-yl)-3-oxoindoline-2-carbonitriles ()
Publication date: 16 March 2017 Source:Tetrahedron, Volume 73, Issue 11 Author(s): Lili Jiang, Xiangjun Peng, Panpan Huang, Zhengwang Chen, Liangxian Liu A method for the combinative oxidative homo dimerization and cyanation of free indole derivatives catalysed by TEMPO along with silver carbonate was demonstrated for the first time This new methodology is both atom and step efficient and is applicable to a broad scope of substrates, allowing the synthesis of a range of synthetically valuable 2-(1H-indol-3-yl)-3-oxoindoline- 2-carbonitriles in moderate to excellent yields. Furthermore, selected compounds 6b and 6g exhibit moderate to good anti-schistosomicidal activities. Graphical abstract image
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