Tetrahedron

Editorial Board ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19
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Synthesis and biological activity of apratoxin derivatives ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Ettore J. Rastelli, Don M. Coltart This review covers the total asymmetric synthesis and biological evaluation of derivatives of the marine natural products known as the apratoxins. Graphical abstract image
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ProteoFind: A script for finding proteins that are suitable for chemical synthesis ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Akira Shigenaga, Naoto Naruse, Akira Otaka ProteoFind is a computational script for finding proteins that are suitable for fragment ligation-based chemical synthesis. This paper describes the development and case studies of ProteoFind, which searches protein lists obtained from the UniProt website. Its application to visualize areas covered by several one-pot three-fragment ligation methods is also discussed. The results demonstrate that ProteoFind not only saves time when searching for synthetic target proteins, but also proposes many candidate proteins from among which biomedically interesting proteins could be found. It also enables clarification of the features of ligation methods by comparing the areas to which each ligation reaction is accessible. Graphical abstract image
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Synthesis of α-benzylated amides via electrocatalytic Favorskii rearrangement of 1, 3-diarylacetones ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Wei Liu, Wei Huang, Tianlei Lan, Haijuan Qin, Cheng Yang Electrolysis of 1,3-diarylacetones with aliphatic amines in Bu4NI/CH3CN to racemic Favorskii amides via benzyl group rearrangement has been developed. The electroconversion is easily conducted in a simple undivided cell under constant-current conditions at room temperature. The electrocatalytic Favorskii rearrangement of 1,3-diarylacetones including electron-withdrawing substituents was favored and gave a good yield of α-benzylated amides. When several unsymmetrical ketones were employed as substrates, this rearrangement with moderate regioselectivity was observed. This chemistry also provides an efficient approach to construct a chiral center at α-position of amides. Graphical abstract image
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Baylis-Hillman acetates in organic synthesis: A simple two-step strategy for oxindole-spiro-α-arylidene-γ-butyrolactone framework ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Deevi Basavaiah, Harathi Lingam, Thelagathoti Hari Babu A facile, convenient, and two step strategy for synthesis of spirooxindoles containing α-arylidene-γ-butyrolactone moiety has been developed via monoalkylation of 2-oxindoles with Baylis-Hillman acetates followed by the spirolactonization of the resulting cinnamic esters on treatment with phenyliodine (III) bistrifluoroacetate (PIFA). Graphical abstract image
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One pot synthesis of aminonaphthoquinone derivatives using Cu(II) immobilized on hyperbranched polyglycerol functionalized graphene oxide as a reusable catalyst under solvent-free conditions ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Hossein Naeimi, Maryam Farahnak Zarabi A new Cu(II) immobilized on hyperbranched polyglycerol (HPG) functionalized graphene oxide catalyst was prepared and characterized by FT-IR, TGA, FE-SEM, XRD, and ICP-OES techniques. This catalyst was used efficiently for the preparation of aminonaphthoquinones via one-pot three-component condensation reaction under solvent-free conditions. The catalyst could be easily recovered and reusable several times without a significant loss of activity, which make this method attractive and in a close agreement with green chemistry. Graphical abstract image
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Iodine-mediated direct synthesis of multifunctional 2-aminobenzimidazoles from N-substituted o-diaminoarenes and isothiocyanates ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Zhen Wang, Qiongli Zhao, Jiao Hou, Wenquan Yu, Junbiao Chang Multifunctional 2-aminobenzimidazoles were directly synthesized through sequential addition of N-substituted o-diaminoarenes to isothiocyanates, formation of carbodiimides via I2-mediated oxidative desulfurization, and intramolecular cycloaddition. This efficient and eco-friendly synthetic process provides a facile access to diverse 2-aminobenzimidazole derivatives from readily accessible substrates under mild reaction conditions in a scalable fashion. Graphical abstract image
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Rhodium(III)-catalyzed CH amination of 2-arylquinazolin-4(3H)-one with N-alkyl-O-benzoyl-hydroxylamines ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Yuanguang Zhang, Jiang Huang, Zhihong Deng, Xunchun Mao, Yiyuan Peng N-benzoate alkylamines were used as the aminating agents, a efficient Rh-catalyzed ortho CH amination of 2-arylquinazolin-4(3H)-one has been reported. The reactions exhibit high efficient and good functional group tolerance. Exclusive 2,6-bis-aminated product and good to excellent yields were obtained under mild reaction conditions. Graphical abstract image
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Combining prolinamides with 2-pyrrolidinone: Novel organocatalysts for the asymmetric aldol reaction ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Ismini Vlasserou, Maria Sfetsa, Dimitrios-Triantafyllos Gerokonstantis, Christoforos G. Kokotos, Panagiota Moutevelis-Minakakis Peptides and especially prolinamides have been identified as excellent organocatalysts for the aldol reaction. The combination of prolinamides with derivatives bearing the 2-pyrrolidinone scaffold, deriving from pyroglutamic acid, led to the identification of novel organocatalysts for the intermolecular asymmetric aldol reaction. The new hybrids were tested both in organic and aqueous media. Among the compounds tested, 22 afforded the best results in petroleum ether, while 25 afforded the products in brine in high yields and selectivities. Then, various ketones and aldehydes were utilized and the products of the aldol reaction were obtained in high yields (up to 100%) with excellent diastereo- (up to 97:3 dr) and enantioselectivities (up to 99% ee). Graphical abstract image
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Regioselective synthesis of 2,3-disubstituted 1-alkyl pyrrolo[2,3-b] quinoxalines through palladium-catalyzed Heck reaction of chalcones and evaluation of their anti-bacterial activities ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Tayebeh Besharati-Seidani, Ali Keivanloo, Babak Kaboudin, Akihiro Yoshida, Tsutomu Yokomatsu The regioselective synthesis of 1-alkyl-2-aryl-3-acyl pyrrolo[2,3-b]quinoxalines through palladium-catalyzed Heck coupling reaction/heteroannulation was reported. The reaction of N-alkyl/benzyl-3-chloroquinoxaline-2-amines with chalcones catalyzed by Pd(OAc)2 in the presence of KOtBu, as the base, in DMSO afforded the desired products in good-to-high yields. The MIC and MBC determinations revealed that these compounds could be used in the future research works for the development of antibiotics. Graphical abstract image
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Transformations of S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones and photochemical properties of reaction products ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Angelina N. Kravchenko, Sergei V. Vasilevskii, Galina A. Gazieva, Vladimir V. Baranov, Valery A. Barachevsky, Olga I. Kobeleva, Olga V. Venidiktova, Valentina A. Karnoukhova For the first time 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were prepared by the reactions of 3-alkylthio-5,7-dimethyl-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-imidazo[4,5-e]-1,2,4-triazin-6(4H)-ones with 3,5-di-tert-butyl-1,2-benzoquinone 1 and 4,6-di-tert-butyl-3-nitro-1,2-benzoquinone 2, respectively. Photochemical transformations of compounds 9 and 10a as well as products of its photooxygenation involving singlet oxygen under UV irradiation: urea 16, isomeric 1,3-dimethyl-4,5-diphenylimidazolidin-2-ones 17 and 17′, and compound 18 were studied by the spectral-kinetic method. Data on the absorption and fluorescence properties of synthesized compounds and their photoproducts were obtained. Graphical abstract image
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Construction of indolenine-substituted spiro[pyrrolidine-2,3′-oxindoles] from 2-alkenylindolenines and isatin-derived azomethine ylides ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Longchen Cui, Guodong Zhu, Siyuan Liu, Xiaoze Bao, Xiangyu Zhao, Jingping Qu, Baomin Wang An organic base-catalyzed 1,3-dipolar cycloaddition between 2-alkenylindolenines and azomethine ylides derived from isatins and benzylamines was successfully developed to assemble indolenine-substituted spiro [pyrrolidine-2,3′-oxindole] ring systems. Generally, good regioselectivities (up to 14:1 rr) and high yields (up to 91%) were obtained under mild conditions. Graphical abstract image
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Total synthesis of viscumneoside III of Viscum coloratum ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Lei Zou, Zixue Zhang, Xiaowen Chen, Hua Chen, Yi Zhang, Jianqi Li, Yu Liu The first total synthesis of viscumneoside III, a promising anti-angina pectoris dihydroflavone O-glycoside isolated from Viscum coloratum was described here. Trichloroaceti-midate was employed as the apiofuranosyl donor to construct the key building block of homoeriodictyol-7-O-β-d-apiosyl-(1 → 2)-β-D-glycoside (1). The longest linear sequence (from 2 to 1) in the synthetic route required thirteen steps and afforded the final product 1 with an overall yield of 6.3%. Graphical abstract image
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One-pot access to indolylchromeno[2,3-b]indoles via iodine-mediated Friedel-Crafts alkylation/oxidative coupling reaction of indoles and salicylaldehydes ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Guang-Qing Rong, Jian-Qiang Zhao, Xiao-Mei Zhang, Xiao-Ying Xu, Wei-Cheng Yuan, Ming-Qiang Zhou An I2-mediated Friedel-Crafts alkylation/oxidative coupling reaction of indoles and salicylaldehydes was developed. With the developed protocol, a series of indolylchromeno[2,3-b]indoles were obtained in good yields (up to 88%) under mild reaction conditions. Two possible reaction mechanisms were tentatively brought forward to account for the formation of the products in light of some control experiments. Graphical abstract image
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Synthesis of 2-(9H-carbazol-1-yl)anilines from 2,3′-biindolyl and ketones ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19 Author(s): Wayland E. Noland, Christopher D. Brown, Abigail E. Zabronsky, Kenneth J. Tritch Twenty-nine examples of 2-(9H-carbazol-1-yl)anilines were obtained in yields from 27 to 95% by refluxing 2,3′-biindolyl (1 equiv.) and ketones (1 equiv.) in ethanolic HCl. Alkyl, cyclic, and aryl ketones were found to be compatible with this method, however, aldehydes are not. Because the reaction proceeds by addition of the carbonyl C atom to the biindolyl 3-position, this method has high regioselectivity. One example is presented of bridging the two N atoms in the carbazolylaniline product with an acetaldehyde synthon to give a benzodiazepino[lm]carbazole. Also, one example is given of installing a dimethylamino group at the α-position of the starting ketone to give an indolo[3,2-c]carbazole. Graphical abstract image
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Graphical Abstract TOC cont'd ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19
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Graphical abstract TOC ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19
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Graphical abstract TOC ()
Publication date: 10 May 2018 Source:Tetrahedron, Volume 74, Issue 19
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Editorial Board ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17
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TBHP/AIBN-Mediated Synthesis of 2-Amino-thioazoles from Active Methylene Ketones and Thiourea under Metal-free Conditions ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Jiyun Sun, Huaibin Ge, Xiaohua Zhen, Xuechan An, Guangtao Zhang, Daisy Zhang-Negrerie, Yunfei Du, Kang Zhao A new oxidative system of tert-butyl hydroperoxide (TBHP)/azodiisobutyronitrile (AIBN) has been used for the first time for a convenient, metal-free synthesis of substituted 2-aminothioazoles from active methylene ketone derivatives and thiourea. The reaction is postulated to proceed via an oxidative cyclization initiated by a radical process and followed by a condensation reaction. Graphical abstract image
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Nematicidal quinone derivatives from three Rubia plants ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Si-Meng Zhao, Bin Kuang, Guang-Zhi Zeng, Zhe Wang, Jia Wang, Xiao-Qiang Chen, Ning-Hua Tan Five new quinone derivatives, rubiasins D-F (1–3), rubialatones A and B (4 and 5), have been isolated from the roots and rhizomes of three Rubia species, Rubia alata, R. wallichiana and R. schumanniana, together with 26 known quinones (6–31). Their structures have been elucidated on the basis of NMR, MS spectra and computational methods. The compounds have been evaluated for their toxicity to the saprophytic nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. Compounds 1, 6 and 7 showed toxicity to C. elegans with the LC50 values at 8.50, 9.44 and 44.82 μg/mL, respectively; and 6 showed toxicity to M. incognita with the LC50 value at 35.22 μg/mL. Meanwhile, compounds 1 and 6 showed inhibitory effect on egg hatch of C. elegans with the LC50 values at 5.60 and 48.95 μg/mL. Graphical abstract image
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Cu-catalyzed reduction of azaarenes and nitroaromatics with diboronic acid as reductant ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Danwei Pi, Haifeng Zhou, Yanmei Zhou, Qixing Liu, Renke He, Guanshuo Shen, Yasuhiro Uozumi A ligand-free copper-catalyzed reduction of azaarenes with diboronic acid as reductant in an aprotic solvent under mild conditions has been developed. Most interestingly, the nitroazaarenes could be reduced exclusively to give the corresponding amines without touching the azaarene moieties. Furthermore, the reductive amination of aromatic nitro compounds and aromatic aldehydes has also been realized. A series of hydrogenated azaarenes and secondary amines were obtained with good functional group tolerance. Graphical abstract image
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Enantioselective phospha-Michael reaction of diethyl phosphonate with exocyclic α,β-unsaturated benzocyclic ketones catalyzed by a dinuclear zinc−AzePhenol catalyst ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Na Shao, Yong-Yang Luo, Hui-Jie Lu, Yuan-Zhao Hua, Min-Can Wang The dinuclear zinc complexes as high performance catalysts were used to catalyze phospha-Michael reaction of exocyclic α,β-unsaturated benzocyclic ketones under mild conditions, and the desired products possessing 1-indanones or 1-tetralones skeleton were obtained with excellent enantioselectivities of up to 99%/99% ee and yields of up to 99%. The absolute stereochemistry of the major products catalyzed by (R,R)-L1 was determined to be the (R,R)-configuration by X-ray crystallographic analysis of 3d. A positive nonlinear effect was observed and the possible mechanism was proposed. Graphical abstract image
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Syntheses of cyclopentyl nucleoside (−)-neplanocin A through tetrazole-fragmentation from cyanophosphates ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Hiroki Yoneyama, Kenji Uemura, Yoshihide Usami, Shinya Harusawa We recently reported a novel synthetic method for five-membered unsaturated cyclic compounds from ketones involving cyanophosphates (CPs) under neutral conditions, in which alkylidene carbenes generated through tetrazole-fragmentation undergo [1,5]-CH insertions to produce the target compounds. The present paper describes the use of the tetrazole-fragmentation from CPs for the efficient and practical syntheses of (−)-neplanocin A and a protected tetrol, the latter of which is an important synthetic precursor of both (−)-neplanocin A and its analogues. Furthermore, formation of an unusual dihydropyran derivative was observed during the synthetic study of the tetrol. Graphical abstract image
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Rhodium-catalyzed reactions of 3-diazoindolin-2-imines with enamines and their extensions towards 5H-pyrazino[2,3-b]indoles ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Guorong Sheng, Shicong Ma, Songlin Bai, Jing Qian, Kai Huang, Bo Lang, Ping Lu, Yanguang Wang The rhodium-catalyzed reactions of 3-diazoindolin-2-imines with β-enamino esters furnished 2,3-diaminoindoles in excellent yields with wide functional group tolerance. The synthesized 2,3-diaminoindoles could be converted into 5H-pyrazino [2,3-b]indoles via a sequential dehydrogenation/6π-ERC/aromatization process. Graphical abstract image
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Diastereoselective approach to trans-5-hydroxy-6-substitutedethanone-2-piperidinones: Scalable syntheses of (+)-febrifugine and (+)-halofuginone ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Chen Wang, Yi-Wen Liu, Zhu Zhou, Chang-Mei Si, Xun Sun, Bang-Guo Wei An efficient diastereoselective approach to access trans-5-hydroxy-6-substitutedethanone-2-piperidinones skeleton has been developed through sequential addition-deprotection-cyclization process involving aldimine 6 with substituted acetones. The diastereoselectivity of substitution at C-6 position of 2-piperidinone was controlled by α-siloxyl group and chiral sulfinamide moiety. In addition, the utility of this effective approach is demonstrated by the scalable syntheses of (+)-febrifugine (2) and (+)-halofuginone (4). Graphical abstract image
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Conformational search and spectroscopic analysis of bis-β-d-glucopyranosyl azacrown derivative ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Marta Adamiak, Stanisław Porwański, Anna Ignaczak 1,10-N,N′-bis-(β-d-ureidoglucopyranosyl)-4,7,13-trioxa-1,10-diazacyclopentadecane is a new, recently synthesized compound, which exhibits complexation ability towards drugs. In the present study various theoretical methods, including molecular mechanics, computer simulations, semiempirical and DFT calculations, are applied to find the lowest energy conformers of this molecule in vacuo and in aqueous solution. For the most stable structures the vibrational frequencies as well as the C and H chemical shifts were computed. Along with the theoretical investigation the IR in the KBr discs and the NMR spectra in water and in pyridine were experimentally recorded. It is shown that in the lowest energy structures the two glucosyl units are placed on the same side of the diazacrown ring with their mutual orientations favoring formation of hydrogen bonds. The “open” structure, in which no such hydrogen bonds can be formed, is found to have much higher energy. The computed and measured IR spectra and NMR chemical shifts are compared and discussed in detail. The most stable structures are analyzed with respect to the possible mechanism of complexation of drugs. Graphical abstract image
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Asymmetric ring-opening reaction of azabenzonorbornadienes with phenols promoted by palladium/(R,R)-DIOP complex ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Zhen Xiu He, Yongyun Zhou, Baiqiu Han, Xin Xu, Yun Li, Hongyu Qin, Ruifeng Fan, Ronibala Devi Laishram, Baomin Fan An efficient asymmetric ring opening reaction of azabenzonorbornadienes with various phenols using Palladium/(R,R)-DIOP complex has been demonstrated, the reaction afforded the corresponding products in excellent yields (80–95%) with moderate enantioselectivities (50–64% ees). The syn-configuration of the product was confirmed by the single X-ray crystallography. Graphical abstract image
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A mechanistic investigation of an Iridium-catalyzed asymmetric hydrogenation of pyridinium salts ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17 Author(s): Yuhua Huang, Shaodong Liu, Yizhou Liu, Yonggang Chen, Mark Weisel, R. Thomas Williamson, Ian W. Davies, Xumu Zhang NMR studies of the catalyst, deuteration experiments, mass spectrometry, and isolation and characterization of intermediates, allow us to propose an outer-sphere mechanism for the Iridium-catalyzed asymmetric hydrogenation of N-alkyl-2-arylpyridinium salts. Graphical abstract image
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Graphical abstract TOC continued ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17
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Graphical abstract TOC ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17
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Graphical abstract TOC ()
Publication date: 26 April 2018 Source:Tetrahedron, Volume 74, Issue 17
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Editorial Board ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16
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Asymmetric autocatalysis of pyrimidyl alkanol and related compounds. Self-replication, amplification of chirality and implication for the origin of biological enantioenriched chirality ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Kenso Soai, Tsuneomi Kawasaki, Arimasa Matsumoto We discovered asymmetric autocatalysis in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, where the product 5-pyrimidyl alkanol acts as a highly efficient asymmetric autocatalyst to afford more of itself (Soai reaction). Asymmetric autocatalysis proceeded quantitatively (>99% yield), affording itself as a near enantiomerically pure (>99.5% ee) product. An extremely low enantiomeric excess (ca. 0.00005% ee) can automultiply during three rounds of consecutive asymmetric autocatalysis to >99.5% ee by asymmetric amplification. Circularly polarized light, and inorganic and organic crystals, act as the origin of chirality to trigger asymmetric autocatalysis. Asymmetric autocatalysis has enormous power to recognize and amplify the chirality of hydrogen, carbon, oxygen, and nitrogen isotopomers. Moreover, absolute asymmetric synthesis, i.e., the formation of enantioenriched compounds without the intervention of any chiral factor, is realized by asymmetric autocatalysis. By using designed molecules based on 5-pyrimidyl alkanol, the intramolecular asymmetric control, self-replication, and improvement of chiral multifunctionalized large molecules has been developed by applying asymmetric autocatalysis. Graphical abstract image
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Synthesis of N,N′-bridged azacalixarenes ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Hiroyuki Takemura, Katsuya Sako, Tesuo Iwanaga, Akane Tatsumi, Yukako Mogami, Hiromi Watanabe, Miho Aoki, Shiho Yûki, Yuri Hayano, Mirei Itaka The one-pot reaction between bis(hydroxymethyl)phenol derivatives and diamines or triamines afforded novel azacalixarenes with bridged structures. Basket-type macrocycles of cone conformations, molecules that contained two aza[3.1.1.1]calixarene skeletons connected by a chain, or novel saucer-type azacalixarenes were obtained from the reaction. Structures of some of them were determined by crystallographic analyses. Graphical abstract image
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Copper-facilitated Suzuki-Miyaura coupling for the preparation of 1,3-dioxolane-protected 5-arylthiophene-2-carboxaldehydes ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Tamás Hergert, Bálint Varga, Angelika Thurner, Ferenc Faigl, Béla Mátravölgyi 5-Formyl-2-thiopheneboronic acid is a widely used building block for the synthesis of diverse structures, however, due to a significant instability its transformation to 5-arylthiophene-2-carboxaldehydes by CC couplings could be performed only in low yields. Herein, as a solution, a convenient technique is described for the preparation of 1,3-dioxolane-protected 5-arylthiophene-2-carboxaldehydes via a one-pot borylation–copper(I) chloride co-catalyzed Suzuki-Miyaura coupling reaction. The utilization of the in situ prepared 2-thiopheneboronic ester derivative is allowed by the method developed. Elimination of the crucial, acidic liberation step of boronic acid species resulted in improved yields and purities. In addition, comparison of various aryl bromides is shown to demonstrate the high tolerance of the transformation to functional groups. Graphical abstract image
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Design and synthesis of new carbohydrate-lithocholic acid conjugates linked via 1,2,3-triazole rings ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Claudia I. Bautista-Hernández, Guillermo E. Negrón-Silva, Rosa Santillán, Blanca Ivonne Vergara-Arenas, Deyanira Ángeles-Beltrán, Leticia Lomas-Romero, Diego Pérez-Martínez In this work, we report the synthesis of a novel carbohydrate-lithocholic acid conjugate linked through of 1,2,3-triazole rings and its derivatives in good to excellent yields. The conjugate was synthesized via copper-catalyzed azide−alkyne cycloaddition (CuAAC) from methyl 4,6-O-benzylidene-2,3-di-O-propargyl-α-d-glucopyranoside and methyl 3-azidolithocholate. The structures of all new compounds were properly characterized by infrared (IR), high-resolution mass spectroscopy (HRMS) and one- and two-dimensional nuclear magnetic resonance (NMR). Graphical abstract image
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A chiral pool approach for asymmetric syntheses of both antipodes of equol and sativan ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Chinni Yalamanchili, Amar G. Chittiboyina, Sateesh Chandra Kumar Rotte, John A. Katzenellenbogen, William G. Helferich, Ikhlas A. Khan For the first time, both antipodes of the isoflavans, equol and sativan were synthesized in >98% ee with good overall yields starting from readily available starting materials. The chiral isoflavan, (−)-equol is produced from soy isoflavones, formonentin and daidzein by the action of intestinal bacteria in certain groups of population and other chiral isoflavans are reported from various phytochemical sources. To produce these chiral isoflavans in gram quantities, Evans' enantioselective aldol condensation was used as a chiral-inducing step to introduce the required chirality at the C-3 position. Addition of chiral boron-enolate to substituted benzaldehyde resulted in functionalized syn-aldol products with >90% yield and excellent diastereoselectivity. Functional group transformations followed by intramolecular Mitsunobu reaction and deprotection steps resulted the target compounds, S-(−)-equol and S-(+)-sativan, with high degree of enantiopurity. By simply switching the chiral auxiliary to (S)-4-benzyloxazolidin-2-one and following the same synthetic sequence the antipodes, R-(+)-equol and R-(−)-sativan were achieved. Both enantiomers are of interest from a clinical and pharmacological perspective and are currently being developed as nutraceutical and pharmacological agents. This flexible synthetic process lends itself quite readily to the enantioselective syntheses of other biologically active C-3 chiral isoflavans. Graphical abstract image
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Aminothiazoles and aminothiadiazoles as nucleophiles in aminocarbonylation of iodobenzene derivatives ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Máté Gergely, László Kollár Various 2-, 3- and 4-substituted iodobenzenes were aminocarbonylated using aminothiazole and aminothiadiazole derivatives in palladium-catalysed reaction. The reaction is chemospecific toward the corresponding carboxamides. Consequently, the application of the above N-nucleophiles provided the N-1,3-thiazol-2-yl- and N-1,3,4-thiadiazol-2-ylcarboxamides in moderate to high yields. Due to the facile work-up of the reaction mixture isolated yields of 90% or higher were obtained in most cases. Graphical abstract image
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A dichotomy in the enantioselective oxidation of aryl benzyl sulfides: A combined experimental and computational work ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Maria Annunziata M. Capozzi, Andrea Bottoni, Matteo Calvaresi, Cosimo Cardellicchio Pentafluorobenzyl pentafluorophenyl sulfide is oxidised with moderate e.e. value and a low yield by the usually highly successful oxidation protocol based upon tert-butyl hydroperoxide (TBHP) in the presence of a titanium/hydrobenzoin complex. This disappointing result resisted until the present work, in which the switch of the oxidation agent (from TBHP to cumene hydroperoxide), suggested by our previous computations, yielded the enantiopure sulfoxide. This valuable chiral compound was obtained in good yields (76%) without resorting to a chromatographic separation. DFT computations uncovered that this favourable reactivity was originated by a stabilizing π−π−stacking between the phenyl group of the oxidant and the pentafluorophenyl moiety of the substrate. Graphical abstract image
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Direct synthesis of anthracenes from o-tolualdehydes and aryl iodides through Pd(II)-Catalyzed sp3 CH arylation and electrophilic aromatic cyclization ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Hyojin Park, Kwangho Yoo, Byunghyuck Jung, Min Kim The first direct synthesis of substituted anthracenes from o-tolualdehydes and aryl iodides via a Pd(II)-catalyzed CH arylation using an alcohol-bearing transient directing group and subsequent AgOTf-assisted electrophilic aromatic cyclization is described. New transient directing groups consisting of amino acids and amino alcohols enhanced the reactivity, and the CH arylation was complete in 12 h at 90 °C. By simply changing the silver salt to silver triflate, the one-pot synthesis of anthracene derivatives was carried out using the present reaction conditions. Graphical abstract image
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Cembranoids from Eunicea sp. enhance insulin-producing cells proliferation ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): G. Porras, A.R. Díaz-Marrero, J.M. de la Rosa, L. D'Croz, N. de Pablo, G. Perdomo, I. Cózar-Castellano, J. Darias, M. Cueto Nine new cembranoids 1–9 containing an α–methylene–γ–butyrolactone together with the known diterpenes 10–15 have been isolated from a crude extract of Eunicea sp. and their structures were established by spectroscopic methods. The proliferative effect of six of these compounds on insulin-producing cells (beta–cells) was evaluated. Graphical abstract image
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Catalyst-free photocyclization for the synthesis of spiro-fused aromatic organic semiconductor based on SFX ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Ming-Li Sun, Feng Zhang, Yan Qian, Chang-Jin Ou, Bin Liu, Ling-Hai Xie, Ying Wei, Bao-Yi Ren, Wei Huang A green protocol with catalyst-free photo-induced cyclization for the synthesis of a spiro-fused organic semiconductor molecule based on spiro[fluorene-9,9′-xanthene] (SFX) was developed. The photophysical and electrochemical properties of the spiro-fused compound (DPCzSFX) have been characterized. The results showed that the molecular stability and the property of the charge injecting/transporting were improved due to the cyclization. And the broadening of the emission spectrum in film makes the sipro-fused compound possible for the application as a host in the white phosphorescent organic light-emitting diodes. However, the same reaction for the spirobifluorene-based dipenylamine derivative did not occur under the same condition, which also highlights the importance of the oxygen heteroatom in the ring to the reaction of cyclization. Graphical abstract image
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Facile preparation of 3-substituted 2-quinazolinones via electrogenerated base ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Najwa Sbei, Belen Batanero, Fructuoso Barba, Beya Haouas, Mohamed Lamine Benkhoud, Isidoro Barba A new series of 3,4-disubstituted quinazolin-2-ones, with potential T-type calcium channel antagonist activity, and new 4-methylene-quinazolin-2-ones, promising catalysts as N-heterocyclic olefins, have been prepared in good yield by a simple reaction between 2-aminobenzophenone, or 2-aminoacetophenone, and cyanomethyl anion electrogenerated by acetonitrile reduction at a graphite electrode, followed by the addition of different organic isocyanates and subsequent heterocyclization. Graphical abstract image
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Facile synthesis of perfluoroalkylated fluorenes via a one-pot two-step three-component process ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Zhenhua Sun, Qi Huang, Jing Han, Weimin He, Jie Chen, Yuchen Xu, Hongmei Deng, Min Shao, Hui Zhang, Weiguo Cao The efficient synthesis of perfluoroalkyl-substituted fluorenes directly from indenones, malononitrile and methyl perfluoroalk-2-ynoates via a one-pot two-step three-component cascade process is reported. Up to 12 examples of indenones with various substituents were converted into their corresponding functionalized fluorene derivatives in good to excellent yields. Graphical abstract image
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Isa‒NHC‒catalyzed intermolecular Stetter reaction of aromatic aldehydes with maleimides: An efficient access to 3‒aroylsuccinimides ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Milind M. Ahire, Santosh B. Mhaske An intermolecular Stetter reaction of aromatic aldehydes with maleimides has been developed using thiazolylidene salt derived Isa‒NHC as an efficient organocatalyst. The synthesized Stetter products “3‒aroylsuccinimides” are important building blocks for the synthesis of natural products and bioactive compounds. The reaction conditions are mild, and various substituents on aromatic aldehyde and maleimide nitrogen were tolerated. Graphical abstract image
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Proton transfer process in synthesis of 3-acetyl-4-(substituted ethylenyl)coumarins and chromeno[3,4-c]pyridines ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Abdolali Alizadeh, Reza Mohammadi, Fahimeh Bayat, Long-Guan Zhu The triphenylphosphine mediated reactions of electron-deficient carbon-carbon triple bonds with 3-acetylcoumarins in dichloromethane afford functionalized 3-acetyl-4-(substituted ethylenyl)coumarins. Also, triphenylphosphine-catalyzed three-component cascade annulation reactions of 3-acetylcoumarins, activated acetylenic compounds, and hydrazines or amines provide a straightforward access to 3,5-dihydro-2H-chromeno[3,4-c]pyridine-1,2-dicarboxylates. In these strategies, the main step to the target products is proton transfer process. All products were obtained in good to high yields. Graphical abstract image
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Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Ana-Luiza Lücke, Sascha Wiechmann, Tyll Freese, Martin Nieger, Tamás Földes, Imre Pápai, Mimoza Gjikaj, Arnold Adam, Andreas Schmidt Unstable N-heterocyclic carbenes can be masked and stabilized as pseudo-cross-conjugated hetarenium-carboxylates which decarboxylate on warming. This study deals with the decarboxylation of carboxylates of mesoionic compounds to generate anionic N-heterocyclic carbenes. Lithium sydnone-4-carboxylates were therefore prepared via 4-bromosydnones by halogen-lithium exchange with nBuLi and subsequent treatment with carbon dioxide. Protonation gave the corresponding sydnone-4-carboxylic acids. Thermogravimetric measurements in addition to temperature dependent IR spectroscopy proved the decarboxylation of lithium sydnone-4-carboxylates and formation of the corresponding sydnone anions which can be represented as anionic N-heterocyclic carbenes. In DMSO-d6 solution, water favors the decarboxylation. Calculations have been performed to elucidate the mechanism of the decarboxylation in the absence and presence of water. Graphical abstract image
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Streptopyrazinones A−D, rare metabolites from marine-derived Streptomyces sp. ZZ446 ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16 Author(s): Mengxuan Chen, Weiyun Chai, Rongyao Zhu, Tengfei Song, Zhizhen Zhang, Xiao-Yuan Lian Secondary metabolites from marine-associated actinomycetes are important source for the discovery of novel bioactive compounds. In this study, an actinomycete Streptomyces sp. ZZ446 was isolated from coastal soils and different media were used to culture this isolated marine actinomycete. It has been found that this actinomycete in the liquid medium of 2216 E with sea salt produced five new compounds of streptopyrazinones A−D (1–4) and N-acetyl-l-isoleucine-l-leucinamide (5) as well as six known diketopiperazines (6–11) and one alkaloid (12). Structures of the new compounds were determined by extensive NMR analyses, HRESIMS data, electronic circular dichroism (ECD) calculation, chemical degradation, Marfey's method, and X-ray diffraction analysis. This type of streptopyrazinones A−D (1–4) is rarely found in the natural resources. New compounds 1–5 showed activity in inhibiting the growth of Candida albicans and methicillin-resistant Staphylococcus aureus. Graphical abstract image
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Graphical abstract TOC continued ()
Publication date: 19 April 2018 Source:Tetrahedron, Volume 74, Issue 16
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