Tetrahedron Letters

Editorial board ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52
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Calcium(II) catalyzed regioselective dehydrative cross-coupling reactions: Practical synthesis of internal alkenes and benzopyrans ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Srinivasarao Yaragorla, Abhishek Pareek, Ravikrishna Dada, Abdulrahman I. Almansour, Natarajan Arumugam A simple and operationally easy protocol for the regioselective synthesis of internal alkenes through a dehydrative cross-coupling and direct coupling procedure has been described using the environmentally benign Ca(II) catalyst. Several alkenes and alcohols underwent the coupling reaction under solvent-free conditions in a short time to produce the desired alkenes. This method is further extended to show the application in the synthesis of novel benzopyran molecules through a cascade strategy. Graphical abstract image
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A rapid response colorimetric and ratiometric fluorescent sensor for detecting fluoride ion, and its application in real sample analysis ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Xujun Zheng, Wencheng Zhu, Hua Ai, Yan Huang, Zhiyun Lu A novel naphthalimide-based fluorescent sensor, namely NIMS, is designed and synthesized for fluoride ion detection. NIMS undergoes a desilylation reaction upon addition of F− ion, thereby shows a colorimetric/fluorometric dual-channel spectral response, i.e., a huge ratiometric absorption value of 229nm together with distinct colour change from yellow to blue, and drastically quenched fluorescence as well. Additionally, NIMS shows high selectivity, good sensitivity and rapid response toward F− ion, and could be used in qualitative detection of F− ion in the solid state and quantitative detection F− ion in toothpaste samples. Graphical abstract image
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Convenient, scalable synthesis of 2-methyl-3-(3′,3′-carboxymethylpropyl)-1,4-naphthoquinone, the principal vitamin K urinary metabolite ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Erik S. Goebel, George Barany The ultimate metabolite of vitamin K, 2-methyl-3-(3′,3′-carboxymethylpropyl)-1,4-naphthoquinone (1), has been shown to be biologically active and may be used as a measure of vitamin K levels in the body. We report a facile, five-step synthesis of 1 that requires only two isolated intermediates and a single chromatographic purification, and provides the title product in 26% overall yield. The structure of one of the intermediates was confirmed by X-ray crystallography. Graphical abstract image
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Catalyst free ethylene glycol promoted synthesis of spiro[indene-2,2′-naphthalene]-4′-carbonitriles and spiro[naphthalene-2,5′-pyrimidine]-4-carbonitriles via one-pot three-component reaction ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Garima Khanna, Pooja Saluja, Jitender M. Khurana A facile and convenient procedure for the synthesis of spiro compounds has been described. The procedure involves the one-pot condensation of indane-1,3-dione or 1.3-dimethylbarbituric acid, aromatic aldehydes and cyclohexylidene malononitrile in ethylene glycol at 100°C in absence of any catalyst. The products were obtained in good yields without use of any chromatographic techniques. Graphical abstract image
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Mild and efficient synthesis of isoindigo derivatives catalyzed by Lewis acid ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Meilin Liu, Shaozhong Qiu, Yu Ye, Guodong Yin A mild and efficient ZrCl4-catalyzed synthesis of isoindigo derivatives from isatins and indolin-2-ones in refluxing ethanol is described. A variety of new functionalized isoindigo derivatives are obtained by simple filtration. Lewis acid was first used as catalyst in the synthesis of isoindigo derivatives. Graphical abstract image
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Palladium-catalyzed non-directed CH benzoxylation of simple arenes with iodobenzene dibenzoates ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Li Li, Ying Wang, Tingting Yang, Qian Zhang, Dong Li A palladium-catalyzed non-directed CH benzoxylation of simple arenes with iodobenzene dibenzoates as both benzoxylate source and oxidant has been developed. The catalytic system was greatly promoted by a pyridine ligand. Good functional groups tolerance was showed in both hypervalent iodine reagents and arene substrates, which can be used for synthesis of aryl benzoates through simple aromatic compounds. Graphical abstract image
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Structure revision of trichotoxin, a chlorinated polyketide isolated from a Trichodesmium thiebautii bloom ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Matthew J. Bertin, Paul V. Zimba, Haiyin He, Peter D.R. Moeller NMR-guided fractionation of the lipophilic extract of Trichodesmium thiebautii filaments led to the isolation of a phenyl-containing chlorinated polyketide (1) and an alkyne-containing analog (2). Comparison of spectroscopic and spectrometric data of 1 with the data of the previously reported trichotoxin, strongly suggested that these metabolites were identical and supports a structural revision of trichotoxin and its designation as trichotoxin A. In addition, we report the isolation and characterization of the alkyne-containing analog trichotoxin B (2). Absolute configuration of 1 and 2 is proposed based on spectroscopic comparison to a close structural analog. Graphical abstract image
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Hyperjapones F–I, terpenoid polymethylated acylphloroglucinols from Hypericum japonicum ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Yan-Ping Li, Xing-Wei Yang, Fan Xia, Hui Yan, Wei-Guang Ma, Gang Xu Hyperjapones F–I (1–4), novel terpenoid polymethylated acylphloroglucinols (TPAPs) with three unusual carbon skeletons, were characterized from Hypericum japonicum. Their structures were determined on the basis of comprehensive MS and NMR spectroscopic data. Compounds 1 and 2 could be formed by hybridization of a trimethylated acylphloroglucinol core with a sabinene-type monoterpenoid unit, while compounds 3 and 4 contained a pinene-type monoterpenoid unit in their molecules. Biosynthetically, a key hetero-Diels–Alder mechanism was proposed for the generation of compounds 1–4. Graphical abstract image
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Oxidative amination of benzylic alkanes with nitrobenzene derivatives as nitrogen sources ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Shaofeng Pang, Feng Shi The oxidative amination of inert CH bonds has the potential to fundamentally change chemistry but is severely limited by the low chemo- and regio-selectivity under oxidation conditions. Until now, no efficient methodology for the direct intermolecular amination of terminal sp3-CH bonds to N-alkyl amines has existed. Here, a new concept is proposed for the oxidative amination of the terminal sp3-CH bond in alkanes via the construction of a complex reaction system composed of a carbon-supported Co-Ni bimetallic catalyst, an alkane, nitrobenzene, tert-butyl hydroperoxide and hydrogen. This system allows the reduction of nitrobenzene to aniline and the further oxidative amination of the alkane. Nitrobenzene and toluene derivatives can be successfully transformed into the corresponding N-benzyl aniline derivatives with up to 95% isolated yields, and the reaction shows excellent functional group tolerance. This approach offers a new concept for catalyst design and may strongly promote the study of inert CH bond activation and the synthesis of functional N-containing compounds. Graphical abstract image
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Facile entry into structurally diverse, privileged, (hetero)arene-fused N-alkoxy 3,4-dihydrobenzo[f][1,4]oxazepin-5(2H)-ones ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Alexander Sapegin, Elena Reutskaya, Alexey Smirnov, Mikhail Korsakov, Mikhail Krasavin Rare and highly medicinally relevant N-alkoxy-substituted benzo[1,4]oxazepines have been synthesized conveniently via the base-promoted S N Ar/Smiles rearrangement/S N Ar tandem cyclization of N-alkoxysalicylamides with a range of bis-electrophilic substrates; subsequent de-alkylation gives rise to the respective N-hydroxy versions. The compounds reported herein significantly add to the contemporary arsenal of small molecule tools for drug discovery. Graphical abstract image
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Anti-cancer and anti-inflammatory new vakognavine-type alkaloid from the roots of Aconitum carmichaelii ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Ying Liang, Jian-Lin Wu, Xun Li, Ming-Quan Guo, Elaine Lai-Han Leung, Hua Zhou, Liang Liu, Na Li Vakognavine-type alkaloids are a rare kind of diterpenoid alkaloid isolated from Delphinium and Aconitum species. During our research on the chemical constituents of the roots of Aconitum carmichaelii, a new vakognavine-type alkaloid (1) along with a known vakognavine-type alkaloid, trifoliolasine E (2), and two known hetisine-type alkaloids (3 and 4) were obtained. The structures were elucidated by a combination of high resolution ESI-MS, 1D and 2D NMR spectra. Compound 1 showed strong inhibitory effects on HT-29, SGC-7901, and HepG2 cell lines with IC50 values of 0.948, 0.983, and 3.645μM, respectively, while trifoliolasine E (2) exhibited moderate activities. Compound 1 was also found to dose-dependently inhibit the activity of cyclooxygenase-2 (COX-2) with an IC50 value of 29.75μM. To the best of our knowledge, this is the first report on the bioactivity of vakognavine-type diterpenoid alkaloids. Graphical abstract image
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ZIF-8 nanoparticles as an efficient and reusable catalyst for the Knoevenagel synthesis of cyanoacrylates and 3-cyanocoumarins ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Oleksii Kolmykov, Nassima Chebbat, Jean-Marc Commenge, Ghouti Medjahdi, Raphaël Schneider Zeolitic imidazolate framework (ZIF-8) particles with an average size of ca. 355nm and a specific surface area of 1786m2.g−1 were used as an heterogenous catalyst for the Knoevenagel synthesis of α,β-unsaturated cyanoesters and 3-cyanocoumarins. The preparation of 3-cyanocoumarins was efficiently achieved using DMF as the solvent and conducting the condensation at 80°C. When the reaction was performed in ethanol, only the intermediates α,β-unsaturated cyanoesters were obtained. The ZIF-8 catalyst can be reused up to five times without any degradation in activity. SEM and XRD analyses demonstrate the high stability of ZIF-8 crystals during the recycling test. Graphical abstract image
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Enhancement of self-assembly and gelation ability of N,N’-didodecanoyl ethylenediamine organogelator by terminal functionalization ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Yasutomo Yamamoto, Akane Oyanagi, Akari Miyawaki, Kiyoshi Tomioka Functionalization at the methyl terminals of N,N′-didodecanoyl ethylenediamine was found to provide a much more powerful low molecular-weight gelators. Replacement of the terminal methyl groups of diamides with carboxy groups effectively enhanced the molecular self-assembly. Terminal functionalization enables organogelator to switch to hydrogelator. FTIR spectra and SEM imaging indicated that an intermolecular hydrogen bonding of the central amide groups were not interfered by terminal functional groups. Graphical abstract image
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Naseseazine C, a new anti-plasmodial dimeric diketopiperazine from a marine sediment derived Streptomyces sp. ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Larissa Buedenbender, Tanja Grkovic, Sandra Duffy, D. Ipek Kurtböke, Vicky M. Avery, Anthony R. Carroll A new dimeric diketopiperazine, naseseazine C, and the known naseseazines A and B were isolated from solid culture extracts of an Australian marine sediment derived Streptomyces species. Naseseazine C displayed a new C-6′/C-3 linkage between the two diketopiperazine subunits and showed moderate activity against the chloroquine-sensitive malaria parasite, Plasmodium falciparum (3D7 strain). Graphical abstract image
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Acid promoted dimerization of β-amino-α,β-unsaturated amides affording bis(functionalized) pyrrolinones ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Sho Hirai, Haruyasu Asahara, Nagatoshi Nishiwaki Polysubstituted pyrrolinones were synthesized by the dimerization of 3-amino-2-butenamides via treatment with 0.5equiv p-TsOH under mild reaction conditions, including oxidation and 1,2-migration of the methyl group. This method is practically advantageous compared to the conventional methods for the preparation of pyrrolinones, because it does not require difficult experimental manipulations and special reagents such as metal catalysts and oxidants. Because the structures of β-amino-α,β-unsaturated amides can be easily modified by changing the precursors, β-keto amide and amine, synthesis of diverse pyrrolinones is possible. Graphical abstract image
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Synthetic study of cnicin: Synthesis of the side chain and its esterification ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Manami Kurita, Miho Tanigawa, Shuhei Narita, Toyonobu Usuki Cnicin is a germacranolide sesquiterpene lactone that possesses potent inhibitory activity against the protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis (HAT). Although cnicin has an interesting structure and attractive biological activity, synthetic studies of cnicin have not yet been reported. This report describes the synthesis of the protected side chain carboxylic acid moiety at C8 of cnicin via two routes starting from l-ascorbic acid. In addition, esterification between the synthetic side chain and salonitenolide derivative, which can be achieved via hydrolysis of cnicin and protection of the primary alcohol, was conducted. Thus, a semi-synthesis of cnicin was achieved. Graphical abstract image
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A novel synthesis of halogenated oxa[9]helicenes and dibromo spiro-lactone derivative by the reaction of helical quinones with halogenating regents ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Mohammad Shahabuddin, Mohammad Salim, Masaaki Tomura, Takao Kimura, Michinori Karikomi A new class of halogenated oxa[9]helicene derivatives along with dibromo spiro-lactone were synthesized in excellent yields, and the compounds were successfully characterized by different spectroscopic techniques (e.g. 1H and 13C NMR, HRMS spectroscopy and X-ray crystallography). Graphical abstract image
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Stereoselective synthesis of benzosulfamidate-fused tetrahydroquinazoline scaffold via organocatalytic [4+2] cycloaddition of 2-amino-β-nitrostyrenses of cyclic N-sulfimines ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Jong-Tack Sim, Hanna Kim, Sung-Gon Kim A concise synthetic route to valuable highly functionalized benzosulfamidate-fused tetrahydroquinazoline is presented. The [4+2] cycloaddition of o-N-Cbz-amino-β-nitrostyrene with benzoxathiazine 2,2-dioxide using an imidazole as the catalyst afforded tetrahydroquinazolines with high diastereoselectivities. Furthermore, a chiral quinine-derived squaramide organocatalyst promoted an asymmetric [4+2] cycloaddition reaction, providing enantioenriched benzosulfamidate-fused tetrahydroquinazolines with good enantiopurities (up to 69:31 er). Graphical abstract image
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Lentinulactam, a hirsutane sesquiterpene with an unprecedented lactam modification ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Soleiman E. Helaly, Christian Richter, Benjarong Thongbai, Kevin D. Hyde, Marc Stadler A novel hirsutane-type sesquiterpene with unprecedented modification of the hirsutene scaffold, lentinulactam (1), along with four known metabolites, connatusin A (2), connatusin B (3), 6-hydroxy-2,2-dimethylchroman-4-one (4), and 6-methoxy-2,2-dimethylchroman-4-ol (5) were obtained from the cultures of the basidiomycete fungus Lentinus cf. fasciatus. The absolute configuration of compound 1 was determined on the basis of the NMR spectroscopic data and Mosher ester analysis. The isolation, structure elucidation, and biological evaluation are reported. Lentinulactam (1) is the first hirsutane-type terpenoid containing unusual modification of the hirsutene scaffold represented in 5-6-6 tricyclic skeleton and the bridged lactam ring with an exocyclic double bond. Moreover, lentinulactam (1) represents the first member of hirsutane family having the opposite absolute configuration to those determined for other hirsutanes. Graphical abstract image
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Regioselective one-pot synthesis of 2,3-diaryl-2H-1-benzopyrans via Brønsted acid-catalyzed [4+2] cycloaddition of salicylaldehydes with diarylacetylenes ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Kenta Tanaka, Yosuke Shigematsu, Mayumi Sukekawa, Yujiro Hoshino, Kiyoshi Honda A regioselective one-pot synthesis of 2,3-diaryl-2H-1-benzopyrans from easily available various diarylacetylenes and salicylaldehydes via Brønsted acid-catalyzed [4+2] cycloaddition has been developed. High regioselectivity was observed in the reaction to afford 2-(electron-rich aryl)-3-(electron-poor aryl)-2H-1-benzopyrans in good yields. The present reaction provides versatile access to functionalized 2,3-diaryl-2H-1-benzopyrans, which would be useful as key intermediates for the synthesis of biologically and photochemically active molecules. Graphical abstract image
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Identification of an unexpected shunt pathway product provides new insights into tirandamycin biosynthesis ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Xingwang Zhang, Zhong Li, Lei Du, George E. Chlipala, Patricia C. Lopez, Wei Zhang, David H. Sherman, Shengying Li Tirandamycin K (7), the first linear 7,13;9,13-diseco-tirandamycin derivative, was isolated from the tamI (encoding the TamI P450 monooxygenase) disruption mutant strain (ΔtamI) of marine Streptomyces sp. 307–9. Its chemical structure with relative and absolute configurations was elucidated by a combination of extensive spectroscopic analyses and biosynthetic inferences. Structural elucidation of this unusual compound provides new insights into tirandamycin biosynthesis. Moreover, examination of the biological activity of 7 confirms the essential function of the bicyclic ketal ring for antibiotic activities of tirandamycins. Graphical abstract image
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An expedient synthesis of non-racemic N-alkylated pyrrolidin-2,5-diones and piperidin-2,6-diones as peptidomimetics ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Anne Brethon, Claire Bouix-Peter, Laurence Clary, Jean-François Fournier, Craig S. Harris, Claude Lardy, Didier Roche, Vincent Rodeschini, Sandrine Talano In our hands, access to 2 novel peptidomimetic scaffolds, based on N-alkylated pyrroldin-2,5-diones and piperidin-2,6-diones, proved to be much more challenging than anticipated. In this short communication, we disclose the strategies that we explored and our final route choices to the desired scaffolds with control of both stereocenters. Graphical abstract image
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Multigram scale, chiron-based synthesis of sacubitril ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Yun Wang, Fen-Er Chen, Yong Shi, Wei-Sheng Tian Based on a chiron approach, sacubitril, a neprilysin inhibitor and API of Entresto, was synthesized in 7 steps with an overall yield of 40%. Two chiral centers of sacubitril are easily obtained from the starting material, one inherited and another inverted. Noteworthy steps are an efficient and mild preparation of epoxide from chiral vicinal diol using C4F9SO2F/DBU, and a one-flask preparation of succinic amide from azide. All the reactions are performed on multigram scales. Graphical abstract image
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Asymmetric glycolate alkylation approach towards total synthesis of 8-O.6′ and 8-O.4′-neolignans ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Mukesh Gangar, Mangilal Chouhan, Sandeep Goyal, M. Harikrishnan, R Chandran, Avinash Ittuveetil, Vipin A. Nair The glycolate alkylation approach for the total synthesis of 8-O.6′ and 8-O.4′-neolignans has been optimized affording the natural products with high overall yields and excellent stereoselectivity. The developed approach can be further utilized towards the synthesis of many natural and unnatural neolignans. This is the first approach for the synthesis of neolignans using asymmetric glycolate alkylation approach. Graphical abstract image
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Chemo-/regio-selective synthesis of 2-aryl-3-acetyl-2,4-dihydro-1H-5H-1,5-benzodiazepines using Lewis acid, CeCl3·7H2O ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Liuyan Yin, Lanzhi Wang A unique and efficient method has been developed for the one-pot synthesis of 2-aryl-3-acetyl-2,4-dihydro-1H-5H-1,5-benzodiazepines (4aa–4fa) in good yields using o-phenylenediamine, aromatic aldehyde and 3-butyn-2-one in the presence of a catalytic amount of CeCl3·7H2O in ethanol at ambient temperature. An exclusive chemo-/regio-selective formation of substituted isomers of 2-aryl-3-acetyl-2,4-dihydro-1H-5H-1,5-benzodiazepines was achieved from the different reaction process, by exploiting the strategy based on the variation of electrophilicity of the two electrophilic centers of aromatic aldehyde, 3-butyn-2-one and nucleophilic profiles of substituted o-phenylenediamines. This process offers an easy and efficient synthesis of 2-aryl-3-acetyl-2,4-dihydro-1H-5H-1,5-benzodiazepines in high yields. Graphical abstract image
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Diacetoxyiodobenzene mediated oxidative transformation of thione to disulfides ()
Publication date: 28 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 52 Author(s): Sarangthem Joychandra Singh, Nepram Sushuma Devi We have developed an efficient oxidative transformation of thione to disulfides using diacetoxyiodobenzene (DIB) in acetonitrile at room temperature. This strategy is suited for oxidation of thiols to disulfide also. The present oxidation protocol is mild reaction condition, column free, and a new route for disulfide formation. Graphical abstract image
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Editorial board ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51
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Transition metal-free formal [2+2+2] cycloaddition reactions of alkynes ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Marko Hapke Cyclotrimerization reactions of alkynes and their oligomers with themselves or other heterocumulenes are usually performed by stoichiometric or catalytic mediacy of transition metal complexes. However, a number of transition metal-free variations have appeared, ranging from stepwise cyclizations of alkynes or oligoalkynes under rather drastical reaction conditions to trimeric condensation reactions of ketoalkynes under amine catalysis and finally uncatalyzed cyclizations of oligoalkynes under partially rather mild conditions. Consequentially a range of different reaction conditions and mechanism are involved in these transformations. The presented digest accounts selected examples of such transition metal-free formal [2+2+2] cycloadditions and exemplarily discusses their mechanistic course of action. Graphical abstract image
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Silver-catalyzed organic reactions of isocyanides ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Yeming Wang, Rapolu Kiran Kumar, Xihe Bi The combined chemistry of silver and isocyanides is unique in performance, proved with the number of recent achievements. With the aim of triggering further research in this field, this review assembles and comprehensively summarizes the silver-based reactions of isocyanides. In this review, we especially emphasize the uniqueness of silver catalysis in the activation of isocyanides, the reaction selectivity, and the mechanistic description. Graphical abstract image
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Enantioselective synthesis of diarylcyclopropanecarboaldehydes by organocatalysis ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Xuyun Chen, Yang Yu, Ziyang Liao, Hao Li, Wei Wang An efficient synthetic method for chiral trisubstituted diarylcyclopropanecarboaldehydes has been developed from substituted benzyl chloride and α,β-unsaturated aldehydes. The reactions were catalyzed by chiral amine catalyst under mild condition to afford the chiral diarylcyclopropanecarboaldehydes in good to high yields and up to excellent enantioselectivities. Graphical abstract image
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Stemona-amines F and G, new alkaloids from Stemona tuberosa ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Yukio Hitotsuyanagi, Yoshiyuki Sekiya, Haruhiko Fukaya, Hyun Sun Park, Shu Zhu, Katsuko Komatsu Two new alkaloids, stemona-amines F and G, were isolated from the roots of Stemona tuberosa Lour. (Stemonaceae). The structure of stemona-amine F was determined by X-ray crystallography and that of stemona-amine G was determined by interpretation of spectroscopic data. The absolute structure of stemona-amine F was established by VCD spectroscopy. Graphical abstract image
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A photocaged, cyclopropene-containing analog of the amino acid neurotransmitter glutamate ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Pratik Kumar, David Shukhman, Scott T. Laughlin Substituted cyclopropenes serve as compact biorthogonal appendages that enable analysis of biomolecules in complex systems. Neurotransmitters, a chemically diverse group of biomolecules that control neuron excitation and inhibition, are not among the systems that have been studied using biorthogonal chemistry. Here we describe the synthesis of cyclopropene-containing analogs of the excitatory amino acid neurotransmitter glutamate starting from a Garner’s aldehyde-derived alkyne. The deprotected cyclopropene glutamate was stable in solution but decomposed upon concentration. Appending a light-cleavable group improved the stability of the cyclopropene while simultaneously caging the neurotransmitter. This strategy has the potential to permit deployment of cyclopropene-modified glutamate as a bioorthogonal probe of the neurotransmitter glutamate in vivo with spatiotemporal precision. Graphical abstract image
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Zn(OTf)2-mediated CH activation: An expeditious and solvent-free synthesis of aryl/alkyl substituted quinolines ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Prashant B. Sarode, Sandeep P. Bahekar, Hemant S. Chandak Zinc(II) triflate catalyzed three-component coupling reactions of alkynes, amines and aldehydes leading to the formation of aryl/alkyl substituted quinolines has been described. Notably, the reaction proceeded efficiently and effectively without the use of ligand, co-catalyst, solvent or inert atmosphere. This robust solvent-free process operates under an ambient atmosphere and avoids the use of precious metals, hazardous solvents and harsh reaction conditions. This atom economic process eliminates the waste generated in the multistep synthesis. Additionally, a pseudo three-component Povarov reaction of amines and butanal proceeds under the same green conditions enabling the formation of 2,3-dialkyl quinolines. Graphical abstract image
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Syntheses of trifluoroethylated unsymmetrical 1,3-diynes by using 1,1-dichloro-2,2,2-trifluoroethane ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Jian Zheng, Qing-Yun Chen, Ke Sun, Yangen Huang, Yong Guo Copper-mediated reaction of terminal 1,3-diynes with 1,1-dichloro-2,2,2-trifluoroethane (CF3CHCl2) using ethanolamine as ligand gave trifluoroethylated unsymmetrical 1,3-diynes in moderate to good yields. The reaction were carried out under mild conditions, and were easy to operate. Aryl groups with weak electron-withdrawing group or electron-donating group, and alkyl substitutents at terminal 1,3-diynes were tolerated. Synthesis of a trifluoroethylated conjugated triyne by using this method was demonstrated. Further transformation of the trifluoroethylated unsymmetrical 1,3-diyne to provide trifluoroethyl-substituted 1,2,3-triazole and isoxazole as application examples were successfully realized. Graphical abstract image
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Novel iridal metabolites with hepatoprotective activities from the whole plants of Iris japonica ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Guo-Ru Shi, Xin Wang, Yan-Fei Liu, Chun-Lei Zhang, Gang Ni, Ruo-Yun Chen, De-Quan Yu Three new iridal metabolites, iridojaponal A (1), B (2) and iridojaponal C (3) were isolated from the whole plants of Iris japonica. Their structures were elucidated on the basis of comprehensive spectroscopic data and chemical evidence. Iridojaponal A (1) and B (2) are the first examples of degraded iridals containing only 16 carbons. A plausible biogenetic pathway of 1 and 2 was also proposed. The absolute configuration at C-22 of 3 was determined by CD analysis accordance with Snatzke’s method. Furthermore, In vitro bioactivity assays, compounds 1 and 2 exhibited moderate hepatoprotective activities against APAP-induced HepG2 cell damage at a concentration of 10μM. Graphical abstract image
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Induced production of a new dipeptide with a disulfide bridge by long-term fermentation of marine-derived Trichoderma cf. brevicompactum ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Hiroyuki Yamazaki, Henki Rotinsulu, Ohgi Takahashi, Ryota Kirikoshi, Michio Namikoshi The marine-derived fungus Trichoderma sp. TPU199 (cf. T. brevicompactum), originally isolated from a Palauan red alga, was found to produce unprecedented epipolythiodiketopiperazines, such as gliovirin and pretrichodermamide A. Long-term static fermentation of the strain induced the production of a new dipeptide, dithioaspergillazine A (1), together with aspergillazine A (2) and three anthraquinones (3–5). The structure of 1 was identified as a modified dipeptide possessing a disulfide bridge based on spectroscopic data for 1 and comparisons with those for 2. On the other hand, long-term agitating fermentation of the strain led to the production of the known bisabolane-type sesquiterpene, (+)-12-hydroxysydonic acid (6), which formed the cyclic derivative 7 during HPLC purification under acidic conditions. Compound 1 exhibited cytotoxicity against HCT-15 and Jurkat cells with IC50 values of 13 and 1.3μM, respectively. Compound 2 did not affect the proliferation of these cancer cells up to a concentration of 22μM. Graphical abstract image
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Dual-organocatalytic Michael/Michael/aldol cascade reaction for the asymmetric construction of fully-substituted cyclohexane ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Qiang-Sheng Sun, Hua Zhu, Hua Lin, Yu Tan, Xiao-Di Yang, Xing-Wen Sun, Xun Sun An efficient cascade reaction was developed affording fully-substituted cyclohexane bearing six contiguous stereocenters via Michael/Michael/aldol sequence. This reaction was catalyzed by low loading of dual-organocatalyst, H-bond donor squaramide (0.5mol%) and achiral secondary amine pyrrolidine (10mol%). Good yields (up to 81%), excellent diastereoselectivities (>20:1 in all cases) and enantioselectivities (>99% in all cases) were obtained for a wide array of Michael acceptors. Graphical abstract image
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Simple primary β-amino alcohol catalyzed enantioselective Diels-Alder reaction of 3-hydroxy-2-pyridones ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Toshihisa Takahashi, U.V. Subba Reddy, Yoshihito Kohari, Chigusa Seki, Taniyuki Furuyama, Nagao Kobayashi, Yuko Okuyama, Eunsang Kwon, Koji Uwai, Michio Tokiwa, Mitsuhiro Takeshita, Hiroto Nakano The simple primary β-amino alcohol catalyzed Diels-Alder reaction of 3-hydroxy-2-pyridones as dienes with N-substituted maleimides to provide the highly substituted optically active isoquinuclidines as a single diastereomers in excellent enantioselectivities (up to 98%) with excellent chemical yields (up to 95%) was demonstrated. A range of simple β-amino alcohols were synthesized from the corresponding inexpensive amino acids and their catalytic activity was examined for this reaction. Graphical abstract image
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Synthesis of β-prolinols via [3+2] cycloaddition and one-pot programmed reduction: Valuable building blocks for polyheterocycles ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Jundong Li, Na Lin, Lei Yu, Yandong Zhang A novel two-step synthesis of multisubstituted β-prolinols has been developed, featuring a [3+2] cycloaddition of azomethine ylides and a programmed reduction triggered by the combination of borane and lithium aluminum hydride (LAH). β-Prolinols are shown to be valuable building blocks for polyheterocycles. Graphical abstract image
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Synthesis of substituted imidazopyridines from perfluorinated pyridine derivatives ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Alireza Poorfreidoni, Reza Ranjbar-Karimi 4-Phenylsulfonyl tetrafluoropyridine was reacted with various N-aryl amidines to give the corresponding imidazopyridine systems via an intramolecular nucleophilic aromatic substitution process whilst pentafluoropyridine gave N′-(perfluoropyridin-4-yl)-N-phenylbenzimidamide and 2,3,5,6-tetrafluoro-N-phenylpyridin-4-amine by a competing elimination reaction. Graphical abstract image
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An efficient and stereoselective approach to 14-membered hexaaza macrocycles using novel semicarbazone-based amidoalkylation reagents ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Anastasia A. Fesenko, Alexander N. Yankov, Anatoly D. Shutalev An efficient synthesis of hydrazones of 4-(3-oxobutyl)semicarbazides and 4-(3-oxobutyl)semicarbazones using novel semicarbazone-based amidoalkylation reagents, 1-arylidene-4-[(aryl)(tosyl)methyl]semicarbazides, has been developed. The synthesis involved reaction of the latter with the Na-enolate of acetylacetone, followed by a base-promoted retro-Claisen reaction and treatment of the obtained 4-(3-oxobutyl)semicarbazones with hydrazine or methylhydrazine. The prepared hydrazones were converted stereoselectively into 14-membered cyclic bis-semicarbazones under acidic conditions. Especially high selectivity (trans/cis ⩾97:3) was observed upon the macrocyclization of 4-(3-oxobutyl)semicarbazone hydrazones. A plausible reaction pathway and the stereochemistry of this cyclization were discussed. Graphical abstract image
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An off-the-shelf sensor for colourimetric detection of sulfide ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Alexis Perry, Daniel Miles The cheap, accessible spiropyran nitroBIPS is a sensitive, selective colourimetric sensor for quantitative determination of sulfide in aqueous media at neutral pH. Graphical abstract image
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Periconiasins I and J, two new cytochalasans from an endophytic fungus Periconia sp. ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Jimei Liu, Dewu Zhang, Min Zhang, Xia Liu, Ridao Chen, Jinlian Zhao, Li Li, Nan Wang, Jungui Dai Two new cytochalasans, periconiasin I (1) with 9/6/5 tricyclic ring, and periconiasin J (2) with 5/6/6/5 tetracyclic ring, were isolated from the endophytic fungus Periconia sp. F-31. Their structures including absolute configurations were elucidated through extensive spectroscopic analyses, calculated ECD, and the circular dichroism data of the [Rh2(OCOCF3)4] complex. Compound 1 showed in vitro cytotoxicity against human MCF-7 tumor cell line with an IC50 value of 4.8μM, compound 2 exhibited weak anti-HIV activity with an IC50 value of 25.0μM. Graphical abstract image
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A general Brønsted acid-catalyzed allylation of benzhydryl alcohols ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Ifedi Orizu, Yuri Bolshan Efficient Brønsted acid-catalyzed allylation of benzhydryl alcohols has been developed. The reaction occurs within 5min in the presence of sub-stoichiometric amounts of HBF4·OEt2 to afford the desired products in good to excellent yields. A variety of functional groups were tolerated under the developed conditions including amides, aldehydes, hydroxyl and carboxylic acid. Graphical abstract image
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EDC/DMAP-mediated direct condensation of dicarboxylic acids and diols: A concise synthesis of extra large polyether macrocyclic lactones and their X-ray structures ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Naveen, Srinivasarao Arulananda Babu We report the EDC/DMAP-mediated direct condensation reactions of dicarboxylic acids with diols and synthesis of new classes of 18-48-membered, small and extra-large polyether macrocyclic lactones. The methodology was executed by using various dicarboxylic acids linked via aliphatic, polyether and aromatic linkers and different diols (e.g., (Z)-but-2-ene-1,4-diol, but-2-yne-1,4-diol, 2,2′-thiobis(ethan-1-ol), 2,2′-(benzylazanediyl)bis(ethan-1-ol), 2,2′-oxybis(ethan-1-ol)). The condensation reactions of dicarboxylic acids with diols afforded 1:1 (18-24-membered) and 2:2 (36–48-membered) polyether macrocyclic lactones. The synthesis of small and extra-large polyether macrocyclic lactones was accomplished without using a template and relatively simple reaction conditions. All the reported macrocyclic lactones were separated by column chromatography and characterized by 1H, 13C NMR and HRMS analyses. The solid state (X-ray) structures of representative polyether macrocyclic lactones were also reported. Graphical abstract image
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Novel N-modified glycines based on a (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol skeleton: 1,3-dioxanes and tripodands ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Oana Moldovan, Katalin Albert, Iulia Nagy, Cristina Morar, Carmen Sacalis, Mircea Darabantu Starting from (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol (p-nitrophenylserinol, a waste optical antipode product from chloromycetin production) or its 5-amino-1,3-dioxane derivatives, we report preliminary data concerning the conversion of these optically active substrates into novel N-modified glycines by chemoselective N-monoalkylation with haloacetic ester or acid (X-CH2COOR, X: Cl, Br; R: Et, H) reagents. The results are discussed in terms of the starting material nature (cyclic vs. acyclic), the steric hindrance in the C-substituted 5-amino-1,3-dioxanes determining the reactivity of the amino-group and the stability of the intermediates. The synthesis of the first tripodands incorporating N-modified glycine motifs as peripheral units is also reported. Graphical abstract image
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The synthesis of novel pyrrololactams and their boronate ester derivatives ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Ryan Greenwood, Kay Yeung Pyrrololactams are naturally occurring compounds possessing interesting biological activities. A new methodology to form novel pyrrololactam systems has been developed via a silver-catalysed cycloaddition followed by a lactamisation reaction. Pyrrololactams were then selectively functionalised using iridium-catalysed borylation conditions and subsequently derivatised in Suzuki cross-couplings. Graphical abstract image
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Activated Fuller’s earth as an inexpensive, eco-friendly, efficient catalyst for the synthesis of 5-aryl 1-H-tetrazole via [3+2] cycloaddition of nitriles and sodium azide ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Deelip S. Rekunge, Krishna S. Indalkar, Ganesh U. Chaturbhuj A simple and efficient method for the preparation of 5-aryl 1-H-tetrazoles was developed from various aryl nitriles and sodium azide (NaN3) via [3+2] cycloaddition reaction using activated Fuller’s earth as an efficient heterogeneous catalyst. This catalyst has advantageous of cost, stability, recovery, reusability, and ecological benefits along with high product yield, and mild protocol. Graphical abstract image
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Lewis acid-assisted N-fluorobenzenesulfonimide-based electrophilic fluorine catalysis in Beckmann rearrangement ()
Publication date: 21 December 2016 Source:Tetrahedron Letters, Volume 57, Issue 51 Author(s): Fukai Xie, Chuan Du, Yadong Pang, Xu Lian, Chentao Xue, Yanyu Chen, Xuefei Wang, Maosheng Cheng, Chun Guo, Bin Lin, Yongxiang Liu A microwave-assisted N-fluorobenzenesulfonimide (NFSI)/Lewis acid-catalyzed Beckmann rearrangement was developed. The remarkable promotion to the electrophilicity of NFSI by Lewis acids was illustrated utilizing a series of readily available oxime substrates. The action model between NFSI and Lewis acids was probed by control experiments and theoretical calculations. Graphical abstract image
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