Tetrahedron

Editorial board ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24
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Recent progress toward the total synthesis of humulanolides ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Jing-Chun Han, Xin Liu, Jing Zhao, Shaoping Li, Chuang-Chuang Li The humulanolides are a series of sesquiterpene lactones, most of which have unique and challenging structure. The humulanolides have exhibited anticancer activity. The combinations of fascinating structural motifs and promising pharmacological properties have prompted significant interest in the synthetic community. In this review, we provide a summary of recent progress regarding the total synthesis of humulanolides. Graphical abstract image
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A novel “turn-on” dipyrrin-type fluorescent detector of Zn2+ based on tetraphenylethene ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Yu-Jie Dong, Zhengong Meng, Cheuk-Lam Ho, Wai-Yeung Wong A tetraphenylethene-containing dipyrrin (TPEpy) has been synthesized and its photophysical properties and metal detecting properties have been investigated. TPEpy displays a high selectivity and sensitivity with a detection limit of 8.96 × 10−8 M for Zn2+ in aqueous media. Graphical abstract image
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Acid-mediated domino reaction of ortho-carbonylated alkynyl-substituted arylaldehydes with phenols: Rapid access to fused indeno[2,1-c]chromen-7-one derivatives ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Hongbo Zhu, Ziping Cao, Xin Meng, Laijin Tian, Guang Chen, Xuejun Sun, Jinmao You Acid-mediated domino reaction of ortho-carbonylated alkynyl-substituted arylaldehydes with phenols is described. The implement of this reaction can provide directly a variety of tetracyclic indeno[2,1-c]chromen-7-one products in good yields. The mechanism was proposed to be a domino indanone ring formation/ortho-alkylation of phenols/dehydrated cyclization for the formation of polycyclic skeleton. In addition, several interesting dimeric products containing a pentacyclic scaffold were also afforded stereoselectively albeit in moderate yields. The present transformations feature the use of simple acid catalyst, short reaction time and good substrate scope. Graphical abstract image
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Synthesis of vinylic iodides for incorporation into the C17-C27 fragment of bryostatins ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Thomas Gregson, Eric J. Thomas Vinylic iodides were identified as useful intermediates for the synthesis of the C17-C27 fragment of the bryostatins with control of the geometry of the exocyclic methoxycarbonylmethylene group. Following literature precedent, the Piers (E)-stereoselective addition of tributyltin hydride to an alkynoate followed by ester reduction and tin-iodine exchange gave vinylic iodides that could be used to form the C20-C21 bond of the bryostatins. Chelation controlled addition of lithiated 3-silyloxypropynes to 2-alkoxyaldehydes followed by reductive iodination was used to prepare vinylic iodides that could be used in the complementary assembly of the C21-C22 bond of the bryostatins. Initial studies of the synthesis of intermediates for metathesis studies using metal catalysed reactions of a vinylic iodide for C21-C22 bond formation were complicated by cyclisation reactions. Graphical abstract image
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Cu0-catalysed 1,3-dipolar cycloadditions of α-amino acid derived N,N-cyclic azomethine imines to ynones ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Jona Mirnik, Eva Pušavec Kirar, Sebastijan Ričko, Uroš Grošelj, Amalija Golobič, Franc Požgan, Bogdan Štefane, Jurij Svete A series of 20 CuAIAC reactions between eight 4-acylamino substituted pyrazolidine-3-one-1-azomethine imines and four terminal ynones were performed using Cu0 as catalyst. The corresponding fluorescent cycloadducts were obtained in very high yields upon simple workup. Thus, Cu-metal turned out to be a better catalyst than CuI in terms of yield and ease of isolation. Availability of azomethine imines, mild reaction conditions, and simple workup enable a “click” access to libraries of densely substituted 2,3-dihydro-1H,5H-pyrazolo[1,2-a]pyrazol-1-ones. Reactivity of differently substituted dipoles was evaluated experimentally and by quantum chemical methods (DFT). Graphical abstract image
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Sulfur-mediated C(sp2)–H imidation and 1,2-imidofluorination of vinyl sulfides ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Zhanhui Yang, Shiyi Yang, Muhammad Sohail Haroone, Wei He, Jiaxi Xu A new strategy for the C(sp2)–H imidation and 1,2-imidofluorination of vinylsulfides has been established through simple treatment with N-fluorobis(benzenesulfonyl)imide, which acts as both oxidant and nitrogen source. For alkyl and electron-rich aryl vinylsulfides, alkyl/arylthioenamines are produced in up to 92% total yields. However, for steric and electron-deficient aryl vinylsulfides, 1,2-imidofluorination products are prepared in up to 73% yields. The chemoselectivity is controlled by the steric and electronic effects of aryl substituents. Thionium ions are proposed as key intermediates in the two reactions. Graphical abstract image
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Tertiary amine-catalyzed (3+3) annulations of δ-acetoxy allenoates: Substrate scope, synthetic application and mechanistic insight ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Chunjie Ni, Weiping Zhou, Xiaofeng Tong Herein is reported the formal (3 + 3) annulations of δ-acetoxy allenoates with 1C,3O-bisnucleophiles by using 6’-deoxy-6’-perfluorobenzamido-quinine (5g) as the catalyst, providing rapid access to 4H-pyrans with excellent enantioselectivity. The reaction features wide substrate scope and mild reaction conditions. The utility of this method is demonstrated in highly stereoselective synthesis of the core of calyxin I. Mechanistic experiments suggest the involvement of 3-ammonium-2,4-dienoate intermediate B N . This type of cationic intermediate arises from an addition-elimination process between allenoate substrate and amine catalyst, and is stable enough for isolation and characterization. Mechanistic studies also disclose the crucial role of amide NH of 5g, which is able to not only activate allenoate to facilitate the formation of B N , but enhance the electrophilicity of δ C of B N for nucleophilic attack. Graphical abstract image
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Synthesis and effect on SMMC-7721 cells of new benzo[c, d]indole rhodanine complex merocyanines as PDT photosensitizers ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Mengqi Yan, Junlong Zhao, Dan Sun, Wei Sun, Borui Zhang, Wenting Deng, Dandan Zhang, Lanying Wang Photodynamic therapy (PDT) represents a modern and noninvasive therapeutic approach, however, it relies on the development of photosensitizers. Here five new benzo[c,d]indole rhodamine complex merocyanines (BIRCM) D1-D5, displaying low dark toxicity and significant photo toxicity, were synthesized as PDT photosensitizers, and characterized by 1H NMR, IR, UV–Vis and HRMS. The investigation of their absorption spectra in different solvents showed that the absorption maxima and molar extinction coefficient were in the region 507–679 nm and 0.21 × 104–1.27 × 105 L · mol−1cm−1, respectively. The evaluation of PDT activity showed that only irradiation could not kill SMMC-7721 cells, and the cell survival rate and inhibition rate at the application dose and duration was 92%–87% and 78%–49%, respectively. Especially, using D2, absorbed in the red zone, as photosensitizer for PDT analyzed its effect on SMMC-7721 cells survival, it could be found that the cell survival rate was 92% without irradiating and the cell inhibited rate was 78% under irradiating at concentrations of 2.5 × 10−6 mol/L, displaying low dark toxicity and high photo toxicity, which was valuable for PDT of some microvascular diseases or other superficial diseases. Graphical abstract image
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Direct synthesis of oxazolidin-2-ones from tert-butyl allylcarbamate via halo-induced cyclisation ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Waroton Paisuwan, Thanakrit Chantra, Paitoon Rashatasakhon, Mongkol Sukwattanasinitt, Anawat Ajavakom A novel synthetic pathway towards the 2-oxazolidinone derivatives involving the halo-induced cyclisation of tert-butyl allyl(phenyl)carbamate was successfully developed. Various halogenating reagents were evaluated under different reaction conditions for the reaction optimisation. Interestingly, the synthetic route to 2-oxazolidinone derivatives containing one halogen atom in the aliphatic site or two halogen atoms including the extra halogen atom substituted in the aryl group at the para position, were thoroughly established for all chloro-, bromo- and iodo compounds. Either halo-unsubstituted-aryl oxazolidinone or p-halo-substituted-aryl oxazolidinone could be selectively produced by selecting the appropriate choices of halogenated reagents and reaction conditions e.g. reaction time and temperature. Toloxatone, a commercial antidepressant, was successfully synthesized by using this developed method. Graphical abstract image
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Bi(OTf)3 catalyzed disproportionation reaction of cinnamyl alcohols ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Chieh-Kai Chan, Yu-Lin Tsai, Meng-Yang Chang Bi(OTf)3 catalyzed disproportionation reaction of cinnamyl alcohols provides chalcones and benzyl styrenes. The use of various metal triflates is investigated herein for facile and efficient redox transformation. A plausible mechanism has been proposed. Graphical abstract image
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Novel family of fused tricyclic [1,4]diazepines: Design, synthesis, crystal structures and molecular docking studies ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Ariel Adamski, Dariusz Kruszka, Zbigniew Dutkiewicz, Maciej Kubicki, Adam Gorczyński, Violetta Patroniak An efficient one-pot strategy for the synthesis of a new family of imidazo[1,4]diazepines has been developed and its mechanism has been proposed, which follows a seven-membered ring closure reaction. The condensation of 2- and 4-imidazolecarboxaldehyde with pyrazole amines provides six compounds 1–6, which are based on two types of fused tricyclic scaffolds. All presented compounds were fully spectroscopically characterized and their structure was unambiguously determined by single crystal X-ray crystallography. Molecular docking studies reveal a high similarity between binding modes of diazepines 1, 6 and eticlopride in the dopamine D3 receptor, as well as between enantiomers 2S, 6S and nortriptyline in dopamine transporter DAT. Graphical abstract image
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[2+2+2] cycloaddition reactions of α,β-unsaturated N-arylaldimines, acetylenedicarboxylates and 2-arylidene-1,3-indanediones ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Wen-Juan Yang, Jing Zhang, Jing Sun, Ya-Jing Xie, Chao-Guo Yan The domino [2+2+2] cycloaddition reaction of α,β-unsaturated N-arylaldimines, dialkyl acetylenedicarboxylates and 2-arylidene-1,3-indanediones in dry methylene dichloride at room temperature afforded isomeric 2′-styryl-1,2′,3,4′-tetrahydro-1′H-spiro[indene-2,3′-pyridines] in good yields. Under similar conditions, the reaction of α,β-unsaturated N-arylaldimines with two molecules of dialkyl acetylenedicarboxylates resulted in 1-aryl-6-styryl-1,6-dihydropyridine-2,3,4,5-tetracarboxylates. Additionally, the three-component reaction of α,β-unsaturated N-arylaldimines, dimethylacetylenedicarboxylate and benzoyl cyanide also gave isomeric 1,3-oxazine-4,5-dicarboxylates. Graphical abstract image
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A new binaphthol based hole-transporting materials for perovskite solar cells ()
Publication date: 15 June 2017 Source:Tetrahedron, Volume 73, Issue 24 Author(s): Xueping Zong, Wenhua Qiao, Yu Chen, Zhe Sun, Mao Liang, Song Xue A novel hole-transporting material (Q221) is synthesized by introducing benzyl groups onto the 1,1′-bi-2-naphthol central core as edge chains and bis(4-methoxyphenyl)amine-substituted 9H-carbazole as donor groups. A reference molecule (Q222) is prepared with hexyl edge chains. The introduction of edge chains influences their molecular orbital energy levels. Q221-based CH3NH3PbI3 perovskite solar cells with carbon counter electrode exhibit the highest power conversion efficiency of 10.37% at a low doping level of Li-TFSI/TBP (15 mM/100 mM), and that of Q222-based cells is 8.87%. Q221-based cells doping with Li-TFSI/TBP of 15 mM/100 mM shows much better photovoltaic parameters compared to those doping with Li-TFSI/TBP of 30 mM/200 mM, when aged in ambient air of 30% RH without encapsulation. The new binaphthol based hole-transporting materials shows a great potential in fabricating effective perovskite solar cells. Graphical abstract image
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Editorial board ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23
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“One-pot” cascade approach to 5,6-dihydroindolizines and indolizines from pyrrole-2-carbaldehydes and nitroethylenes ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Wen Zhong, Huajian Zhu, Hongbin Zou Simple and practical reactions of pyrrole-2-carbaldehydes with nitroethylenes provide either the 5,6-dihydroindolizines or the indolizines in one pot, depending on the reaction temperature. Additionally, a plausible mechanism for the entire sequence is proposed. Graphical abstract image
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Hyperfine coupling constants of β-phosphorylated nitroxides: Subtle interplay between steric strain, hyperconjugation, and dipole-dipole interactions ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Paulin Nkolo, Gérard Audran, Paul Bremond, Raphaël Bikanga, Sylvain R.A. Marque, Valérie Roubaud Solvent effects in β-phosphorylated nitroxides show that nitrogen and phosphorus hyperfine coupling constants a N and a P, increase and decrease with increasing polarity, polarizity, and Hydrogen Bond Donor effects of solvents, respectively. In a series of articles, it was shown that the driving interaction controlling the change in a P is the maximization of the N+•—O– … ∙∙∙+PO– dipole – dipole interaction. In this work, we show that the steric strain in spiro β-phosphorylated nitroxides affords the opposite trend for a P, that is, a P increases with increasing solvent properties features. Graphical abstract image
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Total synthesis of TMS-ent-bisabolangelone ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Bernard Riss, Marion Garreau, Prisca Fricero, Patricia Podsiadly, Nicolas Berton, Sophie Buchter The absolute configuration of bisabolangelone has been established by an eleven step total synthesis of the corresponding TMS protected antipode starting from (R)-(+)-pulegone. Comparison of the TMS-derivatives by GC on a chiral column, allowed us to assign the absolute configuration of the synthetic compound and thus of the corresponding natural product. The latter has been confirmed by the Mosher's ester analysis of the known secondary carbinol derivative. Graphical abstract image
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Two new lignan-iridoid glucoside diesters from the leaves of Vaccinium bracteatum and their relative and absolute configuration determination by DFT NMR and TDDFT-ECD calculation ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Yong-Mei Ren, Chang-Qiang Ke, Attila Mándi, Tibor Kurtán, Chunping Tang, Sheng Yao, Yang Ye Two new lignan-iridoid glucoside diesters (2 and 3), together with their putative biosynthetic precursor 10-O-trans-caffeoyl-6α-hydroxyl-dihydromonotropein (1), were characterized from the leaves of Vaccinium bracteatum. Their planar structures and relative configuration were elucidated by spectroscopic measurements and DFT C NMR calculations, and their absolute configurations were determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The plausible biosynthetic pathways of new compounds were also proposed. Graphical abstract image
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Design of 2′-phenylethynylpyrene excimer forming DNA/RNA probes for homogeneous SNP detection: The attachment manner matters ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Kira Astakhova, Andrey V. Golovin, Igor A. Prokhorenko, Alexey V. Ustinov, Irina A. Stepanova, Timofei S. Zatsepin, Vladimir A. Korshun 1-Phenylethynylpyrene fluorophore (1-PEPy) has long-wavelength shifted emission and higher photostability compared to pyrene, retaining, however, pyrene's ability to form excimers. Here we report the synthesis of 2′-O-[3(and 4)-(pyren-1-ylethynyl)benzyl]-uridines and their tandem incorporation into deoxyribo- and 2′-O-Me-ribo-oligonucleotide probes. Excimer forming probes of type NN … NNXXNN … NN (X = 2′-O-[meta(or para)-(pyren-1-ylethynyl)-benzyl]uridine) containing two adjacent fluorescent nucleosides within an oligonucleotide are available in four types (meta-meta; para-meta; meta-para; para-para). Both DNA (N = deoxyribonucleotides) and 2′-O-Me-RNA (N = 2′-O-Me-ribo-nucleotides) probes were synthesized and their hybridization with complementary and singly mismatched DNA and RNA was studied. Several probes show a dramatic response of their excimer-to-monomer intensity ratio upon hybridization. Remarkably, most spectacular fluorescence changes were demonstrated for probes with para-meta and meta-para combination within 2′-O-Me-ribo-oligonucleotides. Using excimer forming probes, three natural SNP in Helicobacter pylori 23S RNA gene (A2144G, A2143G, A2143C) and the wild type gene can be distinguished. Graphical abstract image
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Remarkable regioselectivities in the course of the synthesis of two new Luotonin A derivatives ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Mohamed Atia, Dóra Bogdán, Maryam Brügger, Norbert Haider, Péter Mátyus Ethyl 4-oxo-3,4-dihydroquinazoline-2-carboxylate reacts selectively with trimethylaluminium-activated 2-amino- or 4-aminobenzoic acid ethyl esters to give the corresponding anilides without self-condensation of the aminobenzoate building blocks. After propargylation, the quinazolinones were treated with Hendrickson's reagent, but only the para-substituted ester was found to undergo the expected [4 + 2] cycloaddition reaction, affording a new Luotonin A derivative. A different regioselectivity was observed with the ortho-substituted ester which affords a benzoxazinone under identical conditions. When the ester group in the ortho-substituted intermediate is replaced with a nitrile function, the outcome of the reaction with Hendrickson's reagent depends on the absence or presence of a base (DBU), yielding either a triphenylphosphonium-substituted iminobenzoxazine or a 4-cyano-substituted Luotonin A derivative. Graphical abstract image
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Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Zhanhui Yang, Shiyi Yang, Jiaxi Xu Regiospecific and direct imidation of the methyl C(sp3)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products. Graphical abstract image
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N-heterocyclic carbene-mediated formal [3+3] annulation of isatin-derived α, β-unsaturated acids: Access to functionalized 3,4′-spirooxindole δ-lactones ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Weiguo Zhang, Junyu Xu, Jing Cao, Chao Fang, Jindong Zhu, Tao Lu, Ding Du An in situ activation of isatin-derived α,β-unsaturated acids 2 for the generation of isatin-derived α,β-unsaturated acyl azoliums II was described. The acyl azoliums II were successfully applied to undergo a formal [3 + 3] annulation with 1,3-dicarbonyl compounds to access functionalized 3,4′-spirooxindole δ-lactones 4. A scale-up synthesis and an enantioselective variant of this protocol were also investigated. The stable and easily prepared acids 2 may be further utilized as promising versatile electrophilic 1,3-synthons for divergent synthesis of spirooxindoles. Graphical abstract image
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Specific intramolecular aromatic CH insertion of diazosulfonamides ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Peipei Huang, Zhanhui Yang, Jiaxi Xu The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp3)−H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp2)−H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp2)−H and aliphatic 1,5- and 1,6-C(sp3)−H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp3)−H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp2)−H insertion. Graphical abstract image
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Expanded aromatic carboxylate anion induced molecular sandwich construction via a tetracationic imidazolium macrocycle conversion from molecular box to molecular tweezer ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Zhen-Hua Ma, Huan-Rong Li, Han-Yuan Gong The molecular box, namely cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)-[2](1,4-dimethylene benzene) (1 4+; as PF6 − salt), fold its conformation as molecular tweezer to clip the specific carboxylates with expanded aromatic plane. The binding modes between 1 4+ and carboxylate, namely pseudorotaxane, outside or clipping (i.e., sandwich like), also depend on the location of carboxylate on the large conjugated moiety. These finding develop the usability of 1 4+ and carboxylates as important building block pairs to create non-covalent self-assembly structures. Graphical abstract image
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First total synthesis of glabramycin B and revision of its relative configuration ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Masaoki Yamamoto, Ken Ishigami, Hidenori Watanabe Structural revision of glabramycin B, which is an antibacterial 10-membered lactone isolated from a fermentation broth of Neosartorya glabra, was achieved by enantioselective synthesis of our proposed structure. The correct structure of glabramycin B was presumed on comparison with related compounds, and synthesis of it was succeeded via dianion alkylation, Shiina's lactonization and Stille cross-coupling. By this synthesis, we were able to correct the reported structural misassignment, and to confirm the relative configuration of glabramycin B to be 10S*,11S*,15R*,20S*. Graphical abstract image
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Synthesis of new 2-substituted pyrazolo[5,1-b][1,3]oxazoles via Sonogashira coupling reactions in water ()
Publication date: 8 June 2017 Source:Tetrahedron, Volume 73, Issue 23 Author(s): Mohammad Bakherad, Rahele Doosti, Mahdi Mirzaee, Khosro Jadidi New 2-substituted pyrazolo[5,1-b][1,3]oxazoles are synthesized through the Sonogashira coupling reaction of 2-iodomethyl-6-methylpyrazolo[5,1-b][1,3]oxazole with terminal alkynes in the presence of a palladium catalyst. This process is carried out in the absence of any copper salt, and provides an eco-friendly and efficient method for the synthesis of the products in water in good-to-high yields. Some of the compounds synthesized were screened for their in vitro anti-oxidant activity using the DPPH (2,2-diphenyl-2-picrylhydrazyl) assays. Graphical abstract image
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Editorial board ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22
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Rhodium-catalyzed synthesis of 2,3 – Disubstituted N-methoxy pyrroles and furans via [3+2] cycloaddition between metal carbenoids and activated olefins ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Bharath Kumar Kuruba, Samuel Vasanthkumar, Lourdusamy Emmanuvel For the first time, we report the synthesis of 2-substituted N-alkoxy pyrrole 3-carboxylate and furan 3-carboxylate via Rh-catalyzed [3+2] cycloaddition between α-diazo oxime ether or α-diazo carbonyl compounds with vinyl equivalents in a one-pot process. We have demonstrated ethyl vinyl ether as well as vinyl acetate as vinyl equivalents and both were found to give excellent yields. We have also demonstrated the synthesis of N-alkoxy dihydropyrrole derivatives by carrying out the reaction at low temperature. Graphical abstract image
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Cesium-catalyzed highly regioselective synthesis of (Z)-vinylic selenosulfides via thioselenation of alkynes with unsymmetrical diorganoyl dichalcogenides ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Lifen Peng, Rongzhen Li, Zilong Tang, Jingyang Chen, Rongnan Yi, Xinhua Xu A novel one-pot approach for the synthesis of (Z)-vinylic selenosulfides is demonstrated through the thioselenation of a wide range of alkynes with unsymmetrical diorganoyl dichalcogenides (RSSePh) catalyzed by cesium hydroxide monohydrate, avoiding the use of the transition metal catalyst and the previous preparation of chalcogen alkynes. Other outstanding features include mild reaction conditions, high regio- and stereo-selectivity, excellent yields and wide functional group tolerance. Graphical abstract image
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Mesomeric betaines constructed of quinolinium cations and carboxylate anions separated by thiophene-ethynyl spacers as fluorescent dipoles ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Alexey Smeyanov, Jörg Adams, Eike G. Hübner, Andreas Schmidt 4- and 5-((1-Methylquinolinium-3-yl)ethynyl)thiophene-2-carboxylates were prepared starting from 3-ethynylquinoline which was subjected to a Sonogashira-Hagihara coupling with ethyl 4- and 5-bromothiophenecarboxylates, respectively. Methylation to give the corresponding quinolinium salts, saponification under basic conditions, acidification to give the carboxylic acids, and basification finally yielded the title compounds. Calculations of the frontier orbital profiles confirm the classification of these mesomeric betaines as cross-conjugated systems, as the HOMO is essentially located in the carboxylate group which is connected to the spacer by a nodal position. Fluorescence spectroscopic investigations were performed. Graphical abstract image
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Transition-metal-free trifluoromethylthiolation and difluoromethylthiolation of thiols with trifluoromethanesulfonyl chloride and difluoromethanesulfonyl chloride ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Xia Zhao, Tianjiao Li, Bo Yang, Di Qiu, Kui Lu Triphenylphosphine-mediated metal-free trifluoromethylthiolation and difluoromethylthiolation of thiols by CF3SO2Cl and CHF2SO2Cl to synthesize trifluoromethyl disulfides and difluoromethyl disulfides, respectively, was achieved at room temperature. Iodine generated in situ from iodide facilitated this reaction via the formation of iodotriphenylphosphonium iodide which could serve as a reducing agent in this transformation. Readily available reagents and mild reaction conditions without transition-metals allow this protocol to be more practical than traditional methods. Graphical abstract image
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Mechanistic studies of thiourea-catalyzed cross-dehydrogenative C-P and C-C coupling reactions and their further applications ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Zhiguo Zhang, Kai Gu, Zongbi Bao, Huabin Xing, Qiwei Yang, Qilong Ren Thiourea-based hydrogen bond donor has been recently disclosed by our group to be an efficient organocatalyst for cross-dehydrogenative coupling (CDC) reactions. Here we present a detailed mechanistic study of this reaction using NMR spectroscopy and kinetic isotope effect experiment. The results revealed that α-amino peroxide is the true intermediate within the catalytic cycle, formed via a thiourea-catalyzed rate-determining hydrogen atom transfer (HAT) process. These experimental investigations not only provide somewhat insight into the mechanism of thiourea-catalyzed CDC reactions but also promote their further applications. Graphical abstract image
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Suzuki-Miyaura cross-coupling reaction of aryl chlorides with aryl boronic acids catalyzed by a palladium dichloride adduct of N-diphenylphosphanyl-2-aminopyridine ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Lin-Yan Xu, Chun-Yu Liu, Shi-Yuan Liu, Zhi-Gang Ren, David James Young, Jian-Ping Lang One palladium dichloride adduct of a phosphine-pyridine ligand N-diphenylphosphanyl-2-aminopyridine (L 1 ) [(L 1 )PdCl2] (1) has been prepared and structurally characterized. Compound 1 can be used as an effective catalyst for the Suzuki-Miyaura cross-coupling reactions of unreactive aryl chlorides with aryl boronic acids, and worked much better than its mono- or bidentate phosphine ligands. The reactions with a wide scope of substrates proceeded to give desired products in good to excellent yields. Graphical abstract image
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Synthesis of P(O)-S organophosphorus compounds by dehydrogenative coupling reaction of P(O)H compounds with aryl thiols in the presence of base and air ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Wei He, Xiao Hou, Xinjin Li, Liang Song, Qing Yu, Zhongwei Wang The synthesis method of P(O)-S organophosphorus compounds by dehydrogenative coupling reaction of P(O)H compounds and aryl thiols was developed. The reaction was carried in the presence of a base and air, and exhibited good characters such as metal-free, mild reaction temperature, excellent substrate tolerance and with moderate to good yields. A plausible mechanism was proposed. Graphical abstract image
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Synthesis of macrocyclic conjugated ψ-disacharides via nitrile oxide cycloaddition: Alkenyl chain length controlled unprecedented formation of di-oxa heterocycles from monosaccharides ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Jewel Hossain, Ramalingam Natarajan, Ashish K. Banerjee, Swapan Majumdar Various symmetrical and unsymmetrical isoxazoline embodied chiral macroheterocycles were synthesized from carbohydrate derived oximes. Our result shows that the mode of cycloaddition is dependent on the length and tether present in alkenyl chain of sugar moiety. Thus in some cases inter- and intramolecular cycloaddition of nitrile oxide were observed with high selectivity. The cycloadducts contains two sugar units linked via macrocycles thus they are considered as pseudo-disacharides. The stereochemistry of the newly formed chiral centers was established by 2D-NMR techniques and X-ray crystallographic studies. Graphical abstract image
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Reactivity and substituent effects in the cyclization of N-aryl-2-nitrosoanilines to phenazines ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Zbigniew Wróbel, Karolina Plichta, Andrzej Kwast Reactivity of variously substituted N-aryl-2-nitrosoanilines in the reaction of cyclization leading to phenazine derivatives, carried out in the presence of N,O-bis(trimethylsilyl)acetamide (BSA), was estimated on the base of the observed reaction times. A strong opposite effect of substituents located at position para to the nitroso group and those located para to the amino group in the side ring was observed. Mechanistic explanation, based on the electronic properties of the substituents and their mesomeric effects, was presented. The usefulness of the obtained data for the designed syntheses of phenazines was exposed. Graphical abstract image
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Formation of tricyclo[6.3.0.02,5]undecane derivatives during attempts to make the rumphellatin A–C oxacarbon skeleton ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Marit K. Leiren, Karl W. Törnroos, Leiv K. Sydnes The results of several approaches to make the 4,4,8-trimethyl-12-oxatricyclo[7.2.1.02,5]dodecane motif present in rumphellatins A–C are reported. The strategy adopted involved (9E)-12,12-dimethyl-5-oxatricyclo[8.2.0.04,6]dodec-9-en-11-ol as an intermediate, but when attempts were made to connect the third methyl group to the carbon skeleton by reacting the epoxide with MeLi under boron-trifluoride catalysis, an unprecedented transannular reaction occurred. The desired product was not formed; instead, compounds containing a tricyclo[6.3.0.02,5]undecane moiety were obtained, in one case in better than 70% yield. Graphical abstract image
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Expanding available pyrazole substitution patterns by sydnone cycloaddition reactions ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): A.W. Brown, J.P.A. Harrity We report the use of alkynylsilanes for the regiocontrolled synthesis of pyrazoles from functionalised sydnones. The strategies outlined herein allow a range of pyrazoles to be accessed with substitution patterns that are otherwise not directly obtained with high selectivity by alkyne cycloadditions. Moreover, this study serendipitously highlighted a simple and convenient procedure for the synthesis of aryl monofluoromethyl ethers through the combination of TBAF and dichloromethane. Graphical abstract image
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Preparation of dual responsive low-molecular-weight hydrogel for long-lasting drug delivery ()
Publication date: 1 June 2017 Source:Tetrahedron, Volume 73, Issue 22 Author(s): Ning Tao, Guotao Li, Miaochang Liu, Wenxia Gao, Huayue Wu A novel low-molecular-weight hydrogel (LMWG) was fabricated by oligopeptide and phenylboronic acid to obtain a smart molecular hydrogel with dual glucose and pH response for long-term drug delivery in this study. Dual glucose and pH responsiveness of the blank molecular hydrogel was first evaluated by on-line tracking the dynamics curves using UV spectroscopy. Model drugs of phenformin for antidiabetes and doxorubicin for anticancer were selected to evaluate the drug carry and glucose/pH responsive drug release of the molecular hydrogel. The results showed the drug-loaded LMWG had good sustaining and long-lasting drug delivery in physiological or pathological environment. Graphical abstract image
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Editorial board ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21
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Synthesis of a novel functionalized tricyclic pyrimidine-fused 1,5-benzodiazepine library ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Hamid Reza Qomi, Azizollah Habibi A series of novel tricyclic pyrimidine-fused 1,5-benzodiazepines (PFBZDs) was synthesized using an enaminone-based approach. The key step in the synthetic strategy involves the formation of the CCNMe2 structure on vicinal carbonyl groups of the 1H-1,5-benzodiazepine-2,4(3H,5H)-dione (BZD). The synthesis of pyrimidine-fused 1,5-benzodiazepines was performed by a simple and efficient method in good to excellent yields under mild and green conditions. The β-enaminoamide intermediates were condensed with thiourea and guanidine derivatives to form the corresponding tricyclic PFBZDs. But reaction of aminoguanidine, thiosemicarbazide, 4-phenylthiosemicarbazide and ethane-1,2-diamine with β-enaminoamides didn't produce any desired product and led to recovery of the corresponding starting BZD. Graphical abstract image
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Ferric nitrate-catalyzed aerobic oxidation of benzylic sp3 CH bonds of ethers and alkylarenes ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Chao Hong, Jiaqi Ma, Meichao Li, Liqun Jin, Xinquan Hu, Weimin Mo, Baoxiang Hu, Nan Sun, Zhenlu Shen A simple catalytic oxidation system was developed for the selective aerobic oxidation of structurally diverse benzylic sp3 CH bonds of ethers and alkylarenes. The reactions were performed with Fe(NO3)3·9H2O as the catalyst, KPF6 as the additive and molecular oxygen as the terminal oxidant without any ligands. Under the optimal reaction conditions, a number of isochromans, xanthenes and thioxanthenes can be converted to their corresponding esters or ketones in good to excellent yields. Graphical abstract image
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Redemitting BODIPY boronic acid fluorescent sensors for detection of lactate ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Jon S. Hansen, Thomas Hoeg-Jensen, Jørn B. Christensen Two redemitting BODIPY boronic acid pinacolate derivatives, sensors 1 and 2 were shown to act as excellent and highly selective lactate detectors at physiological pH (7.4), where the formed sensor-lactate complexes exhibited a significant emission and absorption increase. Since hyperlactataemia ([l-lac] > 6.5 mM) is a common complication in intensive care units, there is need for easy, on-line monitoring of lactate levels in patients. Semi-invasive monitoring via a lactate electrode or optic fiber would be attractive. This may beneficially replace existing lactate detection methods requiring a high degree of instrumentation. Sensors 1 and 2 can detect lactate without interference from biological important monosaccharides, such as d-glucose, d-fructose and d-mannose. Graphical abstract image
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Conjugates between minor groove binders and Zn(II)-tach complexes: Synthesis, characterization, and interaction with plasmid DNA ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Claudia Sissi, Luca Dovigo, Maria Laura Greco, Antonella Ciancetta, Stefano Moro, Jakub W. Trzciński, Fabrizio Mancin, Paola Rossi, Giampiero Spalluto, Paolo Tecilla A new family of conjugates between a Zn(II)-tach complex and (indole)2 or benzofuran-indole amide minor groove binders connected through alkyl or oxyethyl linkers of different lengths has been prepared. The conjugates bind strongly to DNA. However, the complexation to DNA to promote the Zn(II) catalyzed hydrolytic cleavage of the DNA results instead in its inhibition. This inhibition effect has been confirmed also using Cu(II). Modeling studies suggest that in the most stable complex conformation, the minor groove binder and the linker lie in the minor groove hampering the interaction between the metal complex and the phosphate backbone of DNA. Therefore, the linear arrangement of minor groove binder-linker-metal complex appears to be effective to ensure tight binding but unproductive from a hydrolytic point of view. Graphical abstract image
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Regio- and diastereoselectivity of the cycloaddition of aldonitrones with benzylidenecyclopropane: An experimental and theoretical study ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Ekaterina V. Sirotkina, Mariia M. Efremova, Alexander S. Novikov, Vladimir V. Zarubaev, Iana R. Orshanskaya, Galina L. Starova, Rafael R. Kostikov, Alexander P. Molchanov 1,3-Dipolar cycloaddition of benzylidenecyclopropane with various aldonitrones proceeds regioselectively giving good yields of 4-spirocyclopropane isoxazolidines. In the case of aldonitrones, bearing carbamoyl- or aryl-groups on the carbon atom, only the cis-isomer is formed. The compounds synthesized were tested for their virus-inhibiting activity. Graphical abstract image
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Cyclometalated Ir(III) complexes-catalyzed aerobic hydroxylation of arylboronic acids induced by visible-light ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Hongcui Yu, Chun Liu, Xiaomei Dai, Jing Wang, Jieshan Qiu The cyclometalated Ir(III) complexes-catalyzed aerobic hydroxylation of arylboronic acids under visible-light has been successfully developed. This catalytic system has a broad substrate scope, affording a series of phenols smoothly with the highest isolated yield up to 95%. Moreover, this protocol is capable to synthesize several useful phenols containing bulky moieties, which are potential candidates or intermediates used as pharmaceuticals and functional materials. The Ir(III)-catalyzed hydroxylation of arylboronic acids could be applied in a one-pot synthesis of several important phenol derivatives, including 1,1′-methylene-bis(2-naphthol), 2,3-dihydro-1H-naphtho[2,1-e][1,3]oxazine and a bioactive compound LUF5771. Graphical abstract image
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Solvent scales comparison by using α-nitrocyclohexanone as probe in ionic liquids, organic solvents and CH3CN/CHCl3 mixtures ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Guido Angelini, Carla Gasbarri The UV–vis spectra of α-nitrocyclohexanone were determined at 25 °C in a series of solvents, including room-temperature ionic liquids, water and CH3CN/CHCl3 binary mixtures. A multiple linear regression analysis was performed by applying the Catalán empirical multiparameter solvent approach. Polarizability plays the major role in the solute-solvent interactions, as demonstrated by the quantification of the single solvent contributions, while an excellent linear correlation was found between the experimental and calculated solvent-dependent maxima adsorption bands. The solvatochromic trend of α-nitrocyclohexanone in the investigated media was confirmed by applying the Spange empirical solvent parameters for the ionic liquids in the Kamlet–Taft scale. Graphical abstract image
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ZnBr2 catalyzed domino Knoevenagel-hetero-Diels–Alder reaction: An efficient route to polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Mostafa Kiamehr, Batoul Alipour, Leyla Mohammadkhani, Behzad Jafari, Peter Langer Various novel polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives were synthesized via domino Knoevenagel-hetero-Diels–Alder reactions of indoline-2-thions and novel N-acrylated anthranilaldehydes in refluxing ethanol as a solvent in the presence of 20 mol% ZnBr2 as a Lewis acid catalyst. All reactions proceed with high yields with excellent regio- and stereoselectivity. Graphical abstract image
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Cytotoxic labdane diterpenes and bisflavonoid atropisomers from leaves of Araucaria bidwillii ()
Publication date: 25 May 2017 Source:Tetrahedron, Volume 73, Issue 21 Author(s): Sherif S. Ebada, Aya N. Talaat, Rola M. Labib, Attila Mándi, Tibor Kurtán, Werner E.G. Müller, AbdelNasser Singab, Peter Proksch Chemical investigation of a methanolic extract of leaves from Araucaria bidwillii (Araucariaceae) from Egypt afforded four new labdane diterpenoidal metabolites (1–4) together with one known diterpene, 7-oxocallitrisic acid (5), two triterpenoidal metabolites, 2-O-acetyl-11-keto-boswellic acid (6) and β-sitosterol-3-O-glucopyranoside (7), phloretic acid (8), and two methylated bisflavonoids, agathisflavone-4′,7,7″-trimethyl ether (9) and cupressuflavone-4′,7,7″-trimethyl ether (10). The new metabolites 1–4 were unambiguously identified by applying extensive 1D and 2D NMR spectroscopic studies as well as HRESIMS. The relative and absolute configurations of 1–4 were determined using ROESY and the modified Mosher's method, respectively. All isolated compounds were assessed for their antimicrobial, antitubercular and cytotoxic activities. Among the tested compounds, the new labdane diterpenes 1–4 revealed significant cytotoxic activity against mouse lymphoma L5178Y cell line with IC50 values ranging from 1.4 to 12.9 μM, respectively. Graphical abstract image
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