Tetrahedron Letters

Editorial Board ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19
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Recent topics in enantioselective acyl transfer reactions with dialkylaminopyridine-based nucleophilic catalysts ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Hiroki Mandai, Kazuki Fujii, Seiji Suga This digest focuses on recent topics in intra- and intermolecular enantioselective acyl transfer reactions with dialkylaminopyridine-based catalysts over the past decade (2007–2017). The structures of the catalysts are divided into four categories according to the location of the chiral environment (C2, C3, or C4 position of pyridine, and miscellaneous). The role of the structure in the enantioselective acyl transfer reaction and the reaction mechanism will be discussed briefly. Graphical abstract image
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Palladium-catalyzed intramolecular vinylarylation of alkene: Access to spirocyclic scaffold ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Longlei Hou, Yifan Wang, Xiaofeng Tong A Pd(0)-catalyzed cascade reaction of (Z)-1-iodo-1,6-diene bearing a N-heteroaryl ring, including indole, pyrrole as well as imidazole, is reported. The reaction proceeds via Heck-type carbopalladation, which is followed by C-H activation of the attached N-hetero ring, thus delivering 6,5-spirocycles in moderate to good yields. Furthermore, the preliminary attempt at asymmetric version was also conducted. Graphical abstract image
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Development of a scalable synthetic route towards a 2,2,6-trisubstituted chiral morpholine via stereoselective hydroalkoxylation ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Chan Woo Huh, Bruce M. Bechle, Joseph S. Warmus A scalable synthetic route towards a chiral 2,2,6-trisubstituted chiral morpholine, which is a known opioid antagonist, was developed. The synthetic route involves incorporating an aryl group via Suzuki-Miyaura coupling and stereoselective hydroalkoxylation catalyzed by trifluoromethanesulfonic acid. Late stage incorporation of both the aryl and N-alkyl groups make this route suitable for further SAR studies on this molecule. Graphical abstract image
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Novel strategy for the preparation of 3-perfluoroalkylated-2H-indazole derivatives ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Hassen Bel Abed, Nils Weißing, Jens Schoene, Jannik Paulus, Norbert Sewald, Marc Nazaré A simple and novel methodology for the synthesis of 3-perfluoroalkylated-2H-indazole derivatives has been elaborated. The perfluoroalkylation of readily available 2-nitrobenzaldimines bearing electron donating groups was performed using the Ruppert-Prakash reagent and its analogues to afford α-difluoromethylated, α-trifluoromethylated and α-pentafluoroethylated benzylamines. A final reductive cyclization mediated by SnCl2·2H2O led to 2H-indazoles containing perfluoroalkyl groups via the generation of a new NN bond in moderate to good yields. Graphical abstract image
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Concise synthesis of polymethoxyflavone sudachitin and its derivatives, and biological evaluations ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Hiroto Sagara, Masaki Kanakogi, Yuki Tara, Hitoshi Ouchi, Junko Kimura, Yukiko Kaneko, Makoto Inai, Tomohiro Asakawa, Tomohisa Ishikawa, Toshiyuki Kan We accomplished a divergent synthesis of sudachitin (2), a polymethoxyflavone isolated from citrus fruits, and six derivatives from acetophenone 9, which was an intermediate in our previous synthesis of nobiletin (1). Compound 2 enhanced glucose-induced insulin secretion in INS-1D cells, but was less potent than 1. Compared with 1, compound 2 and two derivatives were more potent inhibitors of cAMP-specific phosphodiesterase. Graphical abstract image
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Colorimetric determination of Hg2+ via thiosemicarbazide-to-oxadiazole transformation of a coumarin-benzopyrylium dye ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Dae Sung Lim, So Young Park, Keum Saem Hwang, Suk-Kyu Chang A dual signaling reaction-based probe derived from a hybrid coumarin-benzopyrylium dye was developed for Hg2+ signaling. The probe exhibited selective colorimetric Hg2+ signaling via the Hg2+-induced thiosemicarbazide-oxadiazole transformation. Interference from Cu2+ ions was successfully circumvented using a citrate buffer as a masking agent. The detection limit for Hg2+ ions was found to be 1.88 × 10–7 M. Practical application to Hg2+ detection in simulated wastewater was realized using a typical smartphone as a stand-alone data capture and data processing device. Graphical abstract image
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Differentiating alkyne reactivity in the post-Ugi transformations: Access to polycyclic indole-fused frameworks ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Chao Liu, Gaigai Wang, Yingchun Wang, Kristof Van Hecke, Olga P. Pereshivko, Vsevolod A. Peshkov The Ugi adducts prepared from propiolic acids, propargylamines, indole-2-carbaldehydes, and isocyanides were utilized to assemble polycyclic indole-fused frameworks via two consecutive carbocyclizations involving triple bonds. First, the peptidyl position of Ugi adduct underwent potassium carbonate-mediated cyclization onto the triple bond derived from propiolic acid. Then, the position 3 of indole core engaged into gold-catalyzed cyclization onto the propargylamine-originated alkyne, completing the construction of polycyclic core. Graphical abstract image
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Total synthesis of five proline-enriched cyclic heptapeptides from the marine sponge Stylissa carteri ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Yulei Li, Qi Chang, Minghao Wu, Xia Zhao The total synthesis of five naturally occurring cyclic proline-enriched heptapeptides from the marine sponge Stylissa carteri was reported. The five cyclic heptapeptides were synthesized by applying a two-step solid-phase/solution synthesis strategy. The linear heptapeptides were assembled by standard Fmoc chemistry on 2-chlorotrityl chloride resin, cleaved off-resin with acetic acid/trifluoroethanol/dichloromethane to keep side-chain protecting groups intact, and subsequently cyclization was achieved by a solution method. The final products were purified by a preparative RP-HPLC system, and their structures were characterized by HR-QTOF-MS NMR. The spectral data of synthetic peptides were found to be identical to that reported for the natural products. Graphical abstract image
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Raney-Ni catalyzed conversion of levulinic acid to 5-methyl-2-pyrrolidone using ammonium formate as the H and N source ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Ananda S. Amarasekara, Yen Maroney Lawrence Renewable biomass based levulinic acid was converted to 5-methyl-2-pyrrolidone in 94% yield by a Raney-Ni catalyzed process using ammonium formate in aqueous medium and heating at 180 °C for 3 h. The Raney-Ni could be reused for four catalytic cycles with about 10% loss in catalytic activity. In a similar reaction levulinic acid could be converted 1-substituted-5-methyl-2-pyrrolidones in 90–95% yield by using a mixture of formic acid and the corresponding primary amine. Graphical abstract image
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Disilylation of N-(2-Halophenyl)-2-phenylacrylamides with hexamethyldisilane via trapping the spirocyclic palladacycles ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Genhua Xiao, Liang Chen, Guobo Deng, Jianbing Liu, Yun Liang The palladium-catalyzed disilylation of the spirocyclic palladacycles with hexamethylaisilane has been realized. The key spirocyclic palladacycles are generated from N-(2-haloaryl)-2-arylacrylamide via intramolecular Heck reaction and followed remote C-H activation. A range of 3-((trimethylsilyl)methyl)-3-(2-(trimethylsilyl)phenyl)indolin-2-ones are obtained in good to excellent yields from readily available starting material under mild conditions. Graphical abstract image
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Temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse electron-demand cycloaddition with in situ generated ortho-quinone methides ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Kenta Tanaka, Mami Kishimoto, Yujiro Hoshino, Kiyoshi Honda The temperature-controlled divergent synthesis of 4-alkoxy- or 4-alkenyl-chromanes via inverse electron-demand cycloaddition with in situ generated ortho-quinone methides under identical reaction conditions except for thermal condition has been developed. At room temperature, the reaction generated 4-methoxychromanes, whereas the reaction performed at room temperature to 100 °C gave 4-alkenylchromanes. Trifluoromethanesulfonic acid was efficiently suitable in the reaction to give the 4-substituted chromanes. This divergent synthetic strategy exhibits a new method giving carbon–carbon or carbon–oxygen bond by controlling the reaction temperature. Graphical abstract image
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Double bond formation based on nitroaldol reaction and radical elimination: A prototype segment connection method for the total synthesis of nigricanoside A dimethyl ester ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Takayuki Tsunoda, Kenshu Fujiwara, Satoshi Okamoto, Yoshihiko Kondo, Uichi Akiba, Yusuke Ishigaki, Ryo Katoono, Takanori Suzuki During the course of our studies toward the total synthesis of nigricanoside A dimethyl ester, a prototype method for the connection of the left- and right-half segments at the C9′–C10′ double bond was developed using a model system. The method was based on a simple three-step process including: (i) a nitroaldol reaction, (ii) chlorination or thionocarbonylation, and (iii) radical elimination. Graphical abstract image
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Tandem Wittig – Reductive annulation decarboxylation approach for the synthesis of indole and 2-substituted indoles ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Prajesh S. Volvoikar, S.G. Tilve A simple tandem Wittig reaction-reductive decarboxylation route is established for the synthesis of indoles from commercially available o-nitrobenzaldehydes and a stable phosphorane. The method allows access to indoles in a very fast manner without involving any metal or expensive reagents or inert atmosphere. Also 2-substituted indoles are obtained which forms an important core of many biological active compounds. Graphical abstract image
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Facile synthesis of diphenylmethyl esters from 2-diphenylmethoxypyridine using catalytic boron trifluoride·diethyl etherate ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Minh Thanh La, Hee-Kwon Kim A practical method for the direct preparation of diphenylmethyl (DPM) esters from 2-diphenylmethoxypyridine is described. The reaction was readily performed in the presence of a catalytic amount of boron trifluoride-diethyl etherate at room temperature. Using this reaction protocol, various carboxylic acids were converted to DPM esters with high yields. This method is highly effective for the protection of carboxylic acids and the synthesis of DPM esters, and offers a promising approach for facile esterification of a variety of carboxylic acids. Graphical abstract image
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A highly selective coumarin-based chemosensor for the sequential detection of Fe3+ and pyrophosphate and its application in living cell imaging ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Wei Wang, Jian Wu, Qinglei Liu, Yan Gao, Huimin Liu, Bing Zhao A new chemosensor based on coumarin FB has been designed and synthesized for the detection of Fe3+ and PPi. FB displayed a high affinity to Fe3+ in the presence of other competing cations. The resulting FB-Fe3+ complex displayed highly sensitivity to PPi via Fe3+ displacement approach. The Fe3+ and PPi recognition processes is rapid and reversible, the detection limits of FB to Fe3+ and FB-Fe3+ complex to PPi were estimated to be 8.73 × 10−8 M and 1.25 × 10−8 M, respectively. The good biocompatibility of FB enables the investigation of fluorescent response for Fe3+ and PPi in living cells by confocal microscope. A B3LYP/6-31G(d,p) basis set was employed for optimization of FB and FB-Fe3+ complex. Graphical abstract image
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Hantzsch ester triggered metal-free cascade approach to isoindolinones ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Youping Tian, Junmei Wei, Meng Wang, Gaoqiang Li, Feng Xu Disclosed herein is an expedient synthesis of biologically important isoindolinone derivatives from reactions of 2-formylbenzoic acids with various amines. This method operates via a deliberately designed catalyst-free tandem reductive amination/cyclization cascade event triggered by a transfer hydrogenation process with easily available Hantzsch ester as the organic hydride source. The ease of operation, mild reaction conditions, facile accessibility of the starting materials, and easy scalability of the current method distinguish it from the other precedent protocols, thus enable it a practical approach to the syntheses of valuable isoindolinone-incorporated drugs. Graphical abstract image
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Synthesis of 3,4-diarylsubstituted hexahydro-1H-indoles ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Feilong Zhou, Erbao Zhao, Ziqin Yan, Deheng Chen, Yujun Zhao Efficient syntheses of 3,4-diarylsubstituted hexahydro-1H-indoles in good yields with excellent diastereoselectivities were achieved with a two-step protocol comprising an allylic cation mediated nucleophilic addition and an intramolecular cyclization reaction. The N-aryl sulfonyl protecting groups of cyclization products were readily removed to furnish free amines with retention of halogen substitutions and CC double bonds. Graphical abstract image
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Production of acetophenone C-glucosides using an engineered C-glycosyltransferase in Escherichia coli ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19 Author(s): Dawei Chen, Ridao Chen, Kebo Xie, Yangyang Duan, Jungui Dai Eight novel acetophenone mono- and bis-C-glucosides were obtained by whole cells harboring an engineered C-glycosyltransferase. Optimization of the fed-bath process improved the yield of 4a to 0.97 mg/mL with 95% conversion rate, which is 2.9-fold higher than that of the single-bath. Four mono-C-glucosides (1a–4a) exhibited potent SGLT2 inhibitory activities with IC50 values at 10−6 M. These findings provide a cost-effective and practical synthetic strategy to produce structurally diverse and novel bioactive C-glucosides for drug discovery. Graphical abstract image
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Graphical Abstract TOC cont’d ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19
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Graphical abstract TOC ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19
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Graphical abstract TOC ()
Publication date: 9 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 19
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Editorial Board ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18
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Recent advances in the integrated micro-flow synthesis containing photochemical reactions ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Yuma Otake, Hiroyuki Nakamura, Shinichiro Fuse Micro-flow photochemical reactions have great advantage over batch photochemical reactions due to its high light-penetration efficiency. Integrated micro-flow reaction enables efficient synthesis of structurally complex compounds from simple starting materials and it can avoid handling of explosive, toxic, unstable, or odorous intermediates. Combination of micro-flow photochemical reactions with integrated micro-flow synthesis enhances their benefits. Here we summarize recently reported integrated multi-step micro-flow synthesis containing various photochemical reactions. Graphical abstract image
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Urea decomposition: Efficient synthesis of pyrroles using the deep eutectic solvent choline chloride/urea ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Lanfang Hu, Juan Luo, Dan Lu, Qiang Tang A simple and efficient method is reported for the synthesis of pyrroles via condensation of a series of tricarbonyl compounds with ammonia, which was generated in situ from decomposition of the deep eutectic solvent choline chloride/urea. Graphical abstract image
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Cyclic and linear amidine catalysts for the efficient synthesis of cyclic trithiocarbonates from carbon disulfide and episulfides under mild conditions ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Naoto Aoyagi, Takeshi Endo Cyclic and linear amidines effectively catalyzed the reaction of carbon disulfide and episulfides under mild conditions, such as ordinary pressure and ambient temperature, to give the corresponding cyclic trithiocarbonates in high yields. Graphical abstract image
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Concise total synthesis of AB5046A and AB5046B ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Lu-Yao Kong, Qing Cui, Zhong Jin, Xiao-Hua Xu Two naturally occurring rare 5-oxo β-triketones, AB5046A and AB5046B, were efficiently synthesized in five linear steps with overall yields of 36% and 28%, respectively. The synthetic strategy highlighted the readily preparation of the key intermediate, 3-ethoxy-5-hydroxycyclohex-2-enone, from commercially available phloroglucinol. Graphical abstract image
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Application of Tsunoda reagent to the convenient synthesis of drug-like pyrazoles ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Arash Mosallanejad, Olivier Lorthioir The versatility of the under-utilised (cyanomethylene)tributylphosphorane (CMBP, Tsunoda reagent) was demonstrated on two occasions in a drug discovery context. Firstly, the high reactivity of the phosphorane allowed the alkylation of a weakly acidic pyrazole when standard Mitsunobu conditions were unsuccessful. Secondly, the clean reaction profile generally obtained using CMBP allowed the direct use of the crude mixture in a subsequent Suzuki cross coupling. This reagent has utility when isolation of the Mitsunobu reaction product (e.g. containing a boronate) is not desirable. Graphical abstract image
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Unexpected one-step synthesis of 3-benzoyl-2-phenylbenzofurans under Wittig conditions ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Michela Begala, Pierluigi Caboni, Maria João Matos, Giovanna Lucia Delogu The reaction of 2-hydroxybenzyltriphenylphosphonium bromide with substituted benzoyl chlorides under Wittig conditions, led to 2-phenylbenzofuran derivatives 4a–p and the unexpected formation of 3-benzoyl-2-phenylbenzofuran derivatives 5a–p. Benzoyl chlorides possessing electron-withdrawing groups afforded 3-benzoyl-2-phenylbenzofuran derivatives in higher yields than those with electron-donating groups. This reaction represents a simple and regioselective, one-pot route towards the preparation of deactivated 3-benzoyl-2-phenylbenzofuran compounds which are difficult to obtain by the direct acylation of 2-phenylbenzofurans. Graphical abstract image
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Synthesis of self-doped polyaniline bearing phosphonic acid moiety via Pd-catalyzed phosphonation of poly(2-bromoaniline) ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Toru Amaya, Tomohiro Hatai, Izumi Kurata, Toshikazu Hirao Self-doped conducting polyaniline bearing phosphonic acid moiety was synthesized via the Pd-catalyzed phosphonation of poly(2-bromoaniline) as a key reaction. Graphical abstract image
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Silver-mediated radical aryltrifluoromethylthiolation of activated alkenes by S-trifluoromethyl 4-methylbenzenesulfonothioate ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Xia Zhao, Bo Yang, Aoqi Wei, Jianqiao Sheng, Miaomiao Tian, Quan Li, Kui Lu Herein, we describe the preparation of trifluoromethylthiol-substituted oxindoles by silver-mediated aryltrifluoromethylthiolation of activated alkenes, using S-trifluoromethyl 4-methylbenzenesulfonothioate as a F3CS radical source and showing that the reagent availability, mild conditions, and broad functional group compatibility of this transformation make it a viable alternative strategy of constructing Csp3 SCF3 bonds. Graphical abstract image
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Development of one-pot benzylic amination reactions of azine N-oxides ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Menekşe Liman, Yunus Emre Türkmen An efficient one-pot synthetic methodology has been developed for the benzylic amination reactions of methyl-substituted azine N-oxides that operate under mild conditions. The reaction was found to tolerate quinoline and isoquinoline N-oxides with electron donating and withdrawing substituents as the electrophilic reaction partners as well as a broad range of nucleophilic primary, secondary and aromatic amines, affording the benzylic amination products in up to 82% yield. Graphical abstract image
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Phosphinate selective hosts and importance of CH hydrogen bonding for affinity modulation toward anion guests ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Dae Hyup Sohn, Eunbi Han, Seung Joo Cho, Jongmin Kang Even though phosphinate and its analogs are very important guests in nature, the artificial receptors which are capable of selective recognition of phosphinate are rare. Here, we report a series of acetate and phosphinate selective hosts (1, 2 and 3) which utilize amide NH and aliphatic CH groups as hydrogen bonding donors. In this series of receptors, even though the amide NH hydrogen bonding element was found to be the most significant, by varying the polarity of CH group, the magnitude of recognition could be modulated considerably. The affinities of host 3 against all the tested anion guests showed significantly higher affinities compared with those of hosts 1 and 2, and this could be attributed to the difference of CH group polarities among the receptors 1, 2 and 3. Cα-H hydrogen in host 3 is the most highly polarized by the charged pyridinium group. Therefore, it is the strongest host in this series of hosts. From the experiments shown here, we demonstrated the importance of CH hydrogen bonding element as a decisive modulating moiety for anionic recognition. Graphical abstract image
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Total syntheses and endoplasmic reticulum stress suppressive activities of hericenes A−C and their derivatives ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Shoji Kobayashi, Yoshiki Hamada, Takeshi Yasumoto, Yuuki Hashino, Araki Masuyama, Kaoru Nagai We report the syntheses and neuroprotective activities of hericenes and their derivatives against endoplasmic reticulum (ER) stress-dependent cell death. Four natural products, including hericenes A−C and hericenol A, and five synthetic derivatives were synthesized and their protective activities were evaluated. In designing the synthetic derivatives, we focused on the binding position of the fatty chain. Hericenes B and C showed moderate protective activity against thapsigargin-induced ER stress-dependent cell death. In contrast, their regioisomers (with respect to the position of the fatty chain) exhibited higher protective activity against tunicamycin-induced ER stress. This study clearly shows that the number and the binding position of the fatty chain are critical for protective activity against ER stress-dependent cell death. Graphical abstract image
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Direct arylation of tertiary amines via aryne intermediates using diaryliodonium salts ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Zhiang Zhang, Xunshen Wu, Jianwei Han, Wenjun Wu, Limin Wang With a strategy by using diaryliodonium salts as the precursors of benzynes, direct N-arylation of tertiary amines with diaryliodonium salts was reported. Thus, the desired aromatic tertiary amines with a wide range of substituents were synthesized in moderate to excellent yields of 55–91%. Graphical abstract image
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Organocatalytic stereoselective conjugate addition of 3-substituted oxindoles with in situ generated ortho-quinone methides ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Weihong Liang, Wenhao Yin, Tingzhong Wang, Fayang G. Qiu, Junling Zhao A novel method for the stereoselective conjugate addition of 3-substituted oxindoles to in situ generated o-QMs was described. This process was catalyzed efficiently by a cinchonidine-derived squaramide catalyst in oil-water phase, furnishing the corresponding 3,3-disubsituted oxindole derivatives in moderate to high yields (up to 98%) with high stereoselectivities (up to 95% ee, 15.4:1 dr). The utility of this reaction was also investigated by the gram-scale synthesis and derivatization of one of the products. Graphical abstract image
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Solution-processable high-efficiency bis(trifluoromethyl)phenyl functionalized phosphorescent neutral iridium(III) complex for greenish yellow electroluminescence ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Hongxin Li, Peng Tao, Yanan Xu, Xinwen Zhang, Shujuan Liu, Qiang Zhao A novel and highly efficient bis(trifluoromethyl)phenyl functionalized iridium(III) complex is designed and synthesized. The complex shows intensive greenish yellow phosphorescence (525 nm with 563 nm as shoulder), high photoluminescence efficiency (0.90) and moderate full width at half maximum (72 nm). The bulky bis(trifluoromethyl)phenyl moiety introduced into the complex provides the excellent solubility and effective steric hindrance for solution-processed organic light-emitting diodes. The maximum power efficiency and current efficiency of electroluminescence are 4.13 lm/W and 9.54 cd/A, respectively. Graphical abstract image
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Dehydrogenative etherification homocoupling of heterocyclic N-oxides ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Dong Zhang, Kai Qiao, Xin Yuan, Mingwei Zheng, Zheng Fang, Li Wan, Kai Guo A novel approach was developed for the dehydrogenative etherification homocoupling of heterocyclic N-oxides in the presence of silver oxide and PyBroP. Various substrates were well tolerated and the desired products were obtained in moderate to good yields. Generally, this reaction features excellent functional group compatibility, broad substrate scope and good regioselectivity. Graphical abstract image
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Unusual reactivity of upper-rim bridged calix[4]arenes – Friedel–Crafts alkylation via cleavage of the macrocyclic skeleton ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Petr Slavík, Pavel Lhoták Upper-rim bridged derivatives of calix[4]arenes, prepared by the direct introduction of mercury into the meta position of the basic skeleton followed by Pd-catalyzed intramolecular bridging, represent a novel type of calixarenes bearing an additional single bond between the meta positions of neighboring aromatic units. Due to the presence of this short bridge, these compounds exhibit extremely distorted cavities when compared with common calix[4]arenes. As a consequence of highly enhanced inner strain, the bridged compounds can be cleaved under acidic conditions to form open oligomeric species (benzylic type carbocation) that can be used for the Friedel–Crafts alkylation of aromatic compounds. This behavior, never observed in common calix[4]arenes, demonstrates a reasonably amended reactivity invoked by the additional bridge. Graphical abstract image
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Exploring azide-enolate cycloaddition in the synthesis of novel Rufinamide analogs ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): José G. Aguirre-De Paz, Davir González-Calderón, Aydeé Fuentes-Benítes, Carlos González-Romero The exploration of azide-enolate cycloaddition in the synthesis of novel Rufinamide analogs is reported for the first time. A very simple procedure involving the use of β-ketonitriles as dipolarophiles afforded 5-aril/heteroayl Rufinamide derivatives in two steps. Graphical abstract image
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dM-Dim for carboxylic acid protection ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Shahien Shahsavari, Travis Wigstrom, James Gooding, Chase McNamara, Shiyue Fang The 1,3-dithian-2-yl-methyl (Dim) and its analogous groups including dimethyl-Dim (dM-Dim) can provide a new dimension of orthogonality for carboxylic acid protection. They can be deprotected under nearly neutral oxidative conditions. In this paper, the protection of carboxylic acid with dM-Dim, deprotection of dM-Dim ester with sodium periodate, stability of dM-Dim protected carboxylic acid under acidic and basic conditions, and selective deprotection of dM-Dim protected carboxylic acids in the presence of tertiary butyl and methyl esters are presented. Graphical abstract image
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Cytotoxic cytochalasans from Aspergillus flavipes PJ03-11 by OSMAC method ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Yingying Si, Mingxu Tang, Shuang Lin, Gang Chen, Qingmei Feng, Yubo Wang, Huiming Hua, Jiao Bai, Haifeng Wang, Yuehu Pei Two new cytochalasans flavichalasine N (1), flavichalasine O (2), together with six known cytochalasans (3–8), were isolated from Aspergillus flavipes PJ03-11 through the application of OSMAC (one strain many compounds) strategy. Flavichalasine O (2) represented the first example of cytochalasans possessing a nitrogen-oxygen heterocycle at the macrocyclic ring part. Their structures were established on the base of extensive spectroscopic analysis. Compounds 1–4 exhibited significant cytotoxic activities against three human cancer cell lines (THP1, HL-60 and PC3) with IC50 values ranging from 3.00 to 15.10 μM. Graphical abstract image
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Pestalustaines A and B, unprecedented sesquiterpene and coumarin derivatives from endophytic fungus Pestalotiopsis adusta ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Jian Xiao, Li-Bin Lin, Jia-Yao Hu, Dong-Zhu Duan, Wei Shi, Qiang Zhang, Wen-Bo Han, Le Wang, Xiao-Ling Wang Pestalustaines A (1) and B (2), one unique sesquiterpene possessing an unusual 5/6/7-fused tricyclic ring system and one unprecedented coumarin derivative bearing 6/6/5/5-fused tetracyclic ring system, were isolated from the plant-derived Pestalotiopsis adusta. Their structures with absolute configurations were established by extensive NMR analysis, X-ray crystallography, and CD spectra associated with TD-DFT calculation. Hypothetical biosynthetic pathways for compounds 1 and 2 are proposed. Compounds 1 and 2 showed weak to moderate cytotoxic activities against three human tumor cell lines HeLa, HCT116, and A549, whose IC50 values were ranged from 21.01 to 55.43 μM. Graphical abstract image
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Diastereoselective conjugate addition/cyclization/bromination: Access to four stereocenters in a single step ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Junzhuo Liao, Dale G. Drueckhammer A stereoselective tandem conjugate addition reaction with a chiral amine-derived nucleophile is reported in which the enolate intermediate is quenched with 1,2-dibromotetrachloroethane as a mild brominating reagent. X-ray analysis of a subsequent derivative was used to prove the configuration at each of the four newly formed stereocenters. The resulting α-bromoester underwent selective transesterification catalyzed by mild base to allow selective manipulation of the two ester groups of the product. Graphical abstract image
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Solid-phase synthesis of homodetic cyclic peptides from Fmoc-MeDbz-resin ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Shimaa A.H. Abdel Monaim, Gerardo A. Acosta, Miriam Royo, Ayman El-Faham, Beatriz G. de la Torre, Fernando Albericio Cyclic homodetic peptides are very appealing for medicinal chemistry programs. In addition to the high efficiency and selectivity inherently associated with peptides, a cyclic structure totally formed by amide bonds increases their stability under physiological conditions. Here Fmoc-MeDbz-resin was studied for the preparation of these peptides. Our results demonstrate the usefulness of this strategy for the preparation of cyclic “head-to-side chain” peptides through cyclative cleavage (simultaneous cyclization and release from the resin). In contrast, for the synthesis of the “head-to-tail” counterparts, the cyclization-cleavage should be carried out in the presence of thiophenol. Graphical abstract image
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Morita-Baylis-Hillman enal-based triple cascade strategy for anti-selective synthesis of highly functionalized tetrahydropyridines using iminium-enamine catalysis ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18 Author(s): Vijai K. Rai, Fooleswar Verma, Mansingh Satnami, Manorama Singh, Ankita Rai A novel and efficient three-component coupling strategy for stereoselective synthesis of highly substituted tetrahydropyridines (THP) is reported in high yield (83–94%) with excellent diastereoselectivity (95–99%) in favor of anti-isomer. The reaction proceeds via sequential iminium-iminium-enamine mediated formation of three consecutive CC, CC and CN bonds in one-pot through reaction of [E]-α-cyano/nitro unsaturated aldehyde, activated methylene and aldimine/phenyl-N-tosyl-methanimine and opens up a new aspect for the utility of Morita-Baylis-Hillman (MBH) adducts in THP synthesis. Graphical abstract image
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Graphical Abstract TOC cont’d ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18
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Graphical abstract TOC ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18
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Graphical abstract TOC ()
Publication date: 2 May 2018 Source:Tetrahedron Letters, Volume 59, Issue 18
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Editorial Board ()
Publication date: 25 April 2018 Source:Tetrahedron Letters, Volume 59, Issue 17
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