Tetrahedron Letters

Editorial board ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44
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New C2-symmetric six-membered carbene ligands incorporating two hydroxyl groups for palladium-catalyzed deprotonative-cross-coupling processes (DCCP) of sp3 C–H bonds in diarylmethanes ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Bi-Hui Zhou, Chen Wu, Xing-Xiu Chen, Hong-Xia Huang, Lin-Lin Li, Li-Mei Fan, Jie Li A series of novel 3,4,5,6-tetrahydropyrimidinium salts, the precursor of N-heterocyclic carbene, were synthesized in high yields using a two-step procedure starting from commercially available amino alcohols. In situ prepared corresponding carbenes were tested in palladium-catalyzed C(sp3)−H arylation of 4-benzylpyridine with aryl bromides, affording triarylmethane derivatives in high yields. Graphical abstract image
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The influence of distal substitution on the base-induced isomerization of long-chain terminal alkynes ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Innus Mohammad, JiYoung Mun, Amber Onorato, Martha D. Morton, Abdullah I. Saleh, Michael B. Smith When compared to a long-straight chain terminal alkyne, a long chain terminal alkyne with a distal isopropyl unit (isobranched) isomerizes about two times faster when treated with strong base under identical conditions, and appears to follow pseudo first order kinetics. In both cases, equilibration to a 95–97:5–3 mixture of terminal:internal alkyne accompanies isomerization. The difference in rate may be due to an unusual folding of both long-chain alkynes, bringing the distal substituent close to the carbon-carbon-triple bond moiety. The distal isopropyl moiety may provide unanticipated steric hindrance that disrupts such folding, making the propargylic proton more available for reaction with base. Graphical abstract image
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Synthesis, characterization and biological evaluation of purine nucleoside analogues ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Shankaraiah Malthum, Naveen Polkam, Tejeswara Rao Allaka, Kalyani Chepuri, Jaya Shree Anireddy We present a convenient route for the synthesis of C6-amino-C5′-N-cyclopropyl carboxamido-C2-alkynylated purine nucleoside analogues 11a–g via Sonogashira coupling reaction. The nine step synthesis is easy to perform, employing commercially available reagents. Compound 9 is used as key intermediate for the synthesis of analogues 11a–g. Synthetic intermediates and final products are appropriately characterized by IR, 1H NMR, 13C NMR and Mass. The modified nucleoside analogues 11a–g is evaluated for in vitro anticancer activity against MDA-MB-231 and Caco-2 cell lines. Screening data reveals that compounds 11b and 11e displayed potent IC50 value of 7.9, 6.8µg/mL respectively against MDA-MB-231 and of 7.5, 8.3µg/mL respectively against Caco-2 than the standard drug doxorubicin, thus establishing the potential anti-cancer properties of these newer derivatives. Graphical abstract image
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[bmIm]OH catalyzed coupling: Green and efficient synthesis of 2,8 dioxacyclopenta [a] inden-3-one derivatives in an aqua media ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Malik A Waseem, Shireen, Khursheed Ansari, Farah Ibad, Afshan Ibad, Jagdamba Singh, I.R. Siddiqui An efficient recyclable [bmIm]OH catalyzed and aqua mediated eco-compatible synthesis of biologically versatile 2,8 dioxacyclopenta [a] inden-3-one derivatives. Combination of ionic liquid and water has emerged out as a powerful synthetic tool for constructing C–C, C–S and C–O bonds. Disclosed methodology for introducing broad range of 2-iodophenols, 2-iodothiophenols and tetronic acid in basic ionic liquid with predictable high yield will catch the attention of synthetic chemists. This protocol has documented the notable advances and the applications of ionic liquid in heterocyclic synthesis. The chosen strategy illustrates important issues regarding scope, reactivity, product yield, reaction time, reuse and recyclability that will help in designing new synthetic routes for other heterocyclic synthesis. Graphical abstract image
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Analogues of the 2-carboxyl-6-hydroxyoctahydroindole (CHOI) unit from diverging Pd-catalyzed allylations: Selectivity as a function of the double bond position ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Zhongyi Mao, Elisabetta Martini, Guillaume Prestat, Julie Oble, Pei-Qiang Huang, Giovanni Poli Pd-catalyzed allylations of cyclic bis-allylic substrates, carried out either as two separate steps or in a pseudo-domino fashion, can generate 2-carboxyl-hexahydroindoles bearing an unsaturation in different positions. Sequential homologation, and epoxidation or syn-dihydroxylation steps were investigated to access analogues of the bicyclic 2-carboxyl-6-hydroxyoctahydroindole motif of aeruginosins, a family of peptides displaying serine protease inhibitor activity. Graphical abstract image
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Al(III) chloride catalyzed multi-component domino strategy: Synthesis of library of dihydrotetrazolo[1,5-a]pyrimidines and tetrahydrotetrazolo[1,5-a]quinazolinones ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Parteek Kour, Varun P. Singh, Brijmohan Khajuria, Tajinder Singh, Anil Kumar Tetrazolo[1,5-a]pyrimidines are well recognized and valuable scaffolds in drug discovery. In the current manuscript, we demonstrated AlCl3 catalyzed synthesis of series of dihydrotetrazolo[1,5-a]pyrimidines and tetrahydrotetrazolo[1,5-a]quinazolinones via a modified Biginelli type multi-component reaction of 5-aminotetrazole, aldehyde and diverse active methylene components such as acetophenone/alkylacetoacetates/dimedone. This provides an efficient route to construct highly functionalized dihydrotetrazolo[1,5-a]pyrimidines and tetrahydrotetrazolo[1,5-a]quinazolinones directly from readily available starting materials. Graphical abstract image
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Selective functionalization of cyano-phenyl-2-oxazolines using TMPMgCl·LiCl ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Leandro A. Bozzini, João H.C. Batista, Murilo B.M. de Mello, Ricardo Vessecchi, Giuliano C. Clososki Metalated phenyl-2-oxazolines bearing cyano groups can be selectively obtained through the reaction of TMPMgCl·LiCl with the appropriate substrate. Subsequent reaction with different electrophiles furnished the functionalized derivatives in good yields. Density functional theory (DFT) calculations were performed to evaluate the influence of the ring substituents on the acidity of the aromatic hydrogens. Application to the synthesis of novel functionalized phthalides illustrates the great potential of the methodology to the synthesis of bioactive compounds. Graphical abstract image
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Aerobic oxidation of benzyl alcohols through biosynthesized palladium nanoparticles mediated by Oak fruit bark extract as an efficient heterogeneous nanocatalyst ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Hojat Veisi, Saba Hemmati, Mahnaz Qomi In this study, green synthesis of Pd nanoparticles (NPs) is outlined through application of Oak fruit bark extract as a reducing, capping and stabilizing agent. The characteristics and properties of the biosynthesized Pd NPs were revealed by FESEM, EDX, XRD, TEM, UV–Vis, and FT-IR spectroscopies. So that, UV–Vis spectroscopy of the Pd colloidal solution confirmed reduction of Pd ions, and XRD and TEM analysis identified fcc unit cell structure forming 5–7nm spherical Pd NPs. Furthermore, catalytic activity of the prepared catalyst was investigated through aerobic oxidation of alcohols, as model reactions. Catalytic evaluations demonstrated achievement of good yields from primary and secondary benzyl alcohols. In general, the devised synthesis method is advantageous from several perspectives. For example, the synthesized catalysts give high product yields and are efficient, they eliminate the need for surfactant, chemical reductants, ligand and organic solvents, the approach is economically inexpensive, it results in cleaner reaction profiles, application of the simply prepared heterogeneous catalyst is convenient, and the catalyst is recoverable and reusable for at least six times without any significant loss of its catalytic activity. Graphical abstract image
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One-pot synthesis of ortho-acylphenols by palladium-catalyzed phenol C–H addition to nitriles ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Tao-Shan Jiang, Bei Gan, Xi Wang, Xiuli Zhang The regioselective one-pot synthesis of ortho-acylphenols via the palladium-catalyzed addition of phenols to nitriles and subsequent hydrolysis is reported. The acylation reaction proceeded smoothly using the Pd(OAc)2/DMSO system and TFA as the additive. This method also provides a direct strategy for the synthesis of a salicylketoxime scaffold. Graphical abstract image
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Synthesis of functionalized chromene and spirochromenes using l-proline-melamine as highly efficient and recyclable homogeneous catalyst at room temperature ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Sakkani Nagaraju, Banoth Paplal, Kota Sathish, Santanab Giri, Dhurke Kashinath An efficient and recyclable homogeneous catalyst is developed using commercially cheap l-proline and melamine for the synthesis of chromenes and spirochromenes (spirooxindoles) via multicomponent reactions at room temperature. Systematic studies were conducted in order to achieve desired reactivity and recyclability of the catalyst using various α-amino acids and aromatic amines as donor-acceptor pairs. Among the screened combinations, l-proline and melamine (3:1 ratio; 3mol% on total weight) was found to be best catalyst to give the desired products with excellent yields (up to 99%) in very short times (1–15min) at room temperature in DMSO as solvent. The catalyst was recovered by adding EtOAc and reused up to 5 cycles without losing the catalytic activity. Graphical abstract image
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Preparation and reactivity of sterically encumbered organocatalysts and their use in the preparation of (S)-Pregabalin precursors ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Mauro Cortigiani, Alberto Tampieri, Claudio Monasterolo, Andrea Mereu, Mauro F.A. Adamo Herein we describe the preparation of a new class of sterically demanding organocatalysts derived from d-fructose and their use, alongside hitherto unreported doubly quaternarised Cinchona ammonium salts, in the Michael reaction of nitromethane with 4-nitro-5-alkenyl-isoxazoles. Graphical abstract image
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Hydrogenolysis of geminal diazides ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Phillip Biallas, Stefan F. Kirsch The complete hydrogenolysis of compounds containing the geminal diazido functionality is described. Using hydrogen over palladium on charcoal, the diazides are reduced, and primary amines are obtained. For example, aminomalonates and glycines are generated in a straightforward manner. A protocol that provides direct access to acetylated amines derived from 2-amino-1,3-diketones in good to excellent yields, via hydrogenation in the presence of acetic anhydride, is also presented. Graphical abstract image
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Synthesis of symmetrically and unsymmetrically substituted S,S-dialkyl phosphonodithioates ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): David J. Jones, Eileen M. O'Leary, Timothy P. O'Sullivan Herein, we report the synthesis of a range of S,S-dialkyl phosphonodithioates. Symmetrically substituted analogues were readily prepared from the corresponding phosphonic dichlorides in good to moderate yields, while unsymmetrically substituted variants were obtained by a sequential alkylation-deprotection-alkylation strategy. Graphical abstract image
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Corrigendum to “Synthesis and biological evaluation of oxoapratoxin E and its C30 epimer” [Tetrahedron Lett 58 (33) (2017) 3333–3336] ()
Publication date: 1 November 2017 Source:Tetrahedron Letters, Volume 58, Issue 44 Author(s): Ping Wu, Hao Xu, Zhi Li, Yang Zhou, Yingxia Li, Wei Zhang
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Editorial board ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43
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Chemical syntheses of the cochliomycins and certain related resorcylic acid lactones ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Martin G. Banwell, Xiang Ma, Benoit Bolte, Yiwen Zhang, Michael Dlugosch The cochliomycins (7–12) are a group of six resorcylic acid lactones that have recently been isolated from culture broths of marine fungi found in the South China Sea. These natural products have attracted attention as synthetic targets because of (in certain instances) their novel structural features and their capacities to suppress biofouling. This short review summarizes the synthesis of these and some related compounds that have been reported to date, including those developed in the authors’ laboratories. Graphical abstract image
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Organotin-catalyzed regioselective benzylation of carbohydrate trans-diols ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Hengfu Xu, Ying Zhang, Hai Dong, Yuchao Lu, Yuxin Pei, Zhichao Pei A convenient approach to regioselective benzylation of carbohydrate trans-diols was developed, where 0.1equiv. of Bu2SnCl2 and 0.1equiv. of TBABr were used as the catalysts and 2.0equiv. of BnCl was used as the benzylation reagent. In most cases, similar or better benzylation regioselectivities and isolated yields were obtained by using catalytic amounts of Bu2SnCl2, rather than stoichiometric amounts of organotin reagents required. Graphical abstract image
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Copper-catalyzed tandem reaction directed toward synthesis of 2,2-disubstituted quinazolinones from vinyl halides and 2-aminobenzamides ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Kotaro Yamaguchi, Shin-ichi Kawaguchi, Motohiro Sonoda, Shinji Tanimori, Akiya Ogawa A copper-catalyzed tandem reaction with vinyl halides and 2-aminobenzamides has been developed. In this synthetic route, cross-coupling reaction of the amide moiety with vinyl halides initially progresses, followed by hydroamination, to provide 2,2-disubstituted quinazolinone derivatives. Moreover, the tandem reaction is used in a one-pot synthesis beginning with alkyne hydroiodination by PPh3, I2, and H2O. Graphical abstract image
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The formal synthesis of (+)-15-deoxy-Δ12,14-prostaglandin J2: Controlling exo-olefin geometry via SmI2-mediated cyclization ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Kazunori Takahashi, Yuichi Arai, Toshio Honda A synthetic approach of (+)-15d-PGJ2 has been developed. The present method features a stereoselective construction of the olefin unit using SmI2-mediated radical cyclization. The resulting cyclic compound was further utilized by efficient introduction of α and ω chains of prostaglandins to achieve enantioselective formal synthesis of (+)-15d-PGJ2. Graphical abstract image
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Isopropenyl acetate: A cheap and general acylating agent of alcohols under metal-free conditions ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Andrea Temperini, Lucio Minuti, Tommaso Morini, Ornelio Rosati, Francesca Piazzolla Functionalized primary, secondary and tertiary alcohols are efficiently acetylated by isopropenyl acetate and catalytic p-TsOH. Graphical abstract image
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Ruthenium hydride catalyzed silylvinylation of terminal alkynes under ethylene atmosphere at 80psi ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Alexandre D.C. Dixon, Robert J. Wilson, Daniel D. Nguyen, Daniel A. Clark The development of methods for the stereoselective synthesis of polysubstituted 1,3-dienes is a challenge to synthetic chemistry. Herein is reported a selective approach for the synthesis of polysubstituted 1,3-dienes using the ruthenium hydride catalyzed intramolecular silylvinylation of alkynes under 80psi of ethylene gas. This strategy affords a single diene isomer, is applicable to substrates with aryl and alkyl substitution at the propargyl and homopropargyl positions, and has been utilized in the synthesis of 5- and 6-membered oxasilacycles. Graphical abstract image
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New, simple, and efficient method for the synthesis of N-substituted 4-trifluoromethyl-5-(alkan-1-ol)-pyridin-2(1H)-imines ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Mário A. Marangoni, Carlos E. Bencke, Helio G. Bonacorso, Marcos A.P. Martins, Nilo Zanatta A new, simple, and efficient method for the synthesis a novel series of 1-substituted 4-(trifluoromethyl)-5-(alkan-1-ol)-pyridin-2(1H)-imines from the reaction of 3-(5,6-dihydro-4H-pyran-3-yl)-4,4,4-trifluorobut-2-enenitrile and 3-(4,5-dihydrofuran-3-yl)-4,4,4-trifluorobut-2-enenitrile with primary amines – is described. The products were obtained in 29–82% yield. Graphical abstract image
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Highly stereoselective asymmetric aldol routes to tert-butyl-2-(3,5-difluorophenyl)-1-oxiran-2-yl)ethyl)carbamates: Building blocks for novel protease inhibitors ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Arun K. Ghosh, Emilio L. Cárdenas, Margherita Brindisi Enantioselective syntheses of tert-butyl ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate and ((S)-2-(3,5-difluorophenyl)-1-((R)-oxiran-2-yl)ethyl)carbamate are described. We utilized asymmetric syn- and anti-aldol reactions to set both stereogenic centers. We investigated ester-derived Ti-enolate aldol reactions as well as Evans’ diastereoselective syn-aldol reaction for these syntheses. We have converted optically active ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate to a potent β-secretase inhibitor. Graphical abstract image
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Trichothiazole A, a dichlorinated polyketide containing an embedded thiazole isolated from Trichodesmium blooms ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Richard S. Belisle, Christopher W. Via, Tracey B. Schock, Tracy A. Villareal, Paul V. Zimba, Kevin R. Beauchesne, Peter D.R. Moeller, Matthew J. Bertin Mass spectrometry-guided isolation of the lipophilic extract of Trichodesmium bloom material led to the isolation and structure characterization of a new thiazole-containing di-chlorinated polyketide (1). The structure of 1 was deduced using 1D and 2D NMR analysis, high-resolution mass spectrometry analysis and complementary spectroscopic procedures. Trichothiazole A possesses interesting structural features, such as a terminal alkyne, two vinyl chlorides and a 2,4-disubstituted thiazole. Trichothiazole A showed moderate cytotoxicity to Neuro-2A cells (EC50: 13.3±1.1μM). Graphical abstract image
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Concise and efficient synthesis of E-stereoisomers of exo-cyclic carbohydrate enones. Aldol condensation of dihydrolevoglucosenone with five-membered aromatic aldehydes1 Part 1 ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Zbigniew J. Witczak, Roman Bielski, Donald E. Mencer Stereoselective synthesis of exocyclic enones 10–17 via a base-catalyzed direct aldol condensation between dihydrolevoglucosenone 1 and heterocyclic aldehydes 2–9 is described. The reaction is performed under mild conditions and is applicable to variety of heterocyclic aldehydes. E-Steroisomers of exo-cyclic enones are the only products. They are very easy to isolate and were formed in good to excellent (72–88%) yield. 1H NMR, 13C NMR analyses provide the structural assignment and absolute stereochemistry of the condensation products. Single-crystal X-ray diffraction of condensation product 12, additionally supports the structural assignment. Graphical abstract image
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Diisobutylaluminum borohydride: An efficient reagent for the reduction of tertiary amides to the corresponding amines under ambient conditions ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Rachel A. Snelling, Gabriella Amberchan, Angel Resendez, Chris L. Murphy, Lauren Porter, Bakthan Singaram A synthetically simple mixed metal hydride, diisobutylaluminum borohydride [(iBu)2AlBH4], is easily generated from a 1:1 mixture of borane-dimethylsulfide (BMS) and diisobutylaluminum hydride (DIBAL). The reduction of tertiary amides using (iBu)2AlBH4 is complete within five minutes under ambient conditions and the product tertiary amines were isolated in 70–99% yields by a simple acid-base extraction. This new methodology, reported herein, works well for reduction of tertiary aliphatic and aromatic amides as well as lactams to the corresponding amines and product isolation and purification does not require column chromatography. Graphical abstract image
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Single and double A3-coupling (aldehyde-amine-alkyne) reaction catalyzed by an air stable copper(I)-phosphole complex ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): José Ricardo Cammarata, Rocío Rivera, Franmerly Fuentes, Yomaira Otero, Edgar Ocando-Mavárez, Alejandro Arce, Juan M. Garcia An air stable copper(I)-phosphole complex, [CuCl{2,5-bis(2-thienyl)-1-phenylphosphole}2] (1), was utilized as a catalyst in single and double A3-coupling reactions for preparing mono- and bi-propargylamines. A variety of aldehydes, amines and terminal alkynes were tested. Most of these reactions led to formation of the expected propargylamines in good yields using low amounts catalyst and obviating both the use of purified reagents as employ of a glovebox. Graphical abstract image
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Nectrianolins A, B, and C, new metabolites produced by endophytic fungus Nectria pseudotrichia 120-1NP ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Nanang Rudianto Ariefta, Priska Kristiana, Handojo Hadi Nurjanto, Hiroyuki Momma, Eunsang Kwon, Tatsuya Ashitani, Keitaro Tawaraya, Tetsuya Murayama, Takuya Koseki, Hiroshi Furuno, Narandulam Usukhbayar, Ken-ichi Kimura, Yoshihito Shiono Two sesquiterpene-epoxycyclohexenone conjugates, nectrianolins A (1) and B (2), together with a sesquiterpene, nectrianolin C (3), were isolated from the brown rice culture of Nectria pseudotrichia 120-1NP, an endophytic fungus isolated from Gliricidia sepium. Their structures were determined on the basis of 1D-/2D-NMR spectroscopy and HRESIMS data analyses in combination with chemical means. Nectrianolins A–C (1–3) exhibited cytotoxic activity against both HL60 and HeLa cells. Graphical abstract image
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Synthesis and computational analysis of conformationally restricted [3.2.2]- and [3.2.1]-3-azabicyclic diamines ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Sreedhar Reddy Tummalapalli, Rohit Bhat, Craig Waitt, Henk Eshuis, David P. Rotella Conformational restriction is a useful approach for ligand design in organic and medicinal chemistry. This manuscript reports the facile synthesis and in silico conformational analysis of two new diastereomeric [3.2.2]-3-azabicyclic, two new [3.2.1]-3-aza-8-oxy-bicyclic and one new [3.2.1]-3-azabicyclic diamine scaffolds. A conformational analysis of these structures along with calculation of carbon–carbon/carbon–nitrogen bond angles was carried out and compared to those in the flexible 1,3-diaminopropane template upon which they were based. It is of particular importance that these scaffolds have bond lengths and angles that can overlap with low energy conformers of the flexible diamine. Such information is useful for ligand design in organic chemistry and for development of structure activity relationships and in silico screening in medicinal chemistry. Graphical abstract image
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A selective hydration of nitriles catalysed by a Pd(OAc)2-based system in water ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Daniel D. Sanz Sharley, Jonathan M.J. Williams In situ formation of a [Pd(OAc)2bipy] (bipy=2,2′-bipyridyl) complex in water selectively catalyses the hydration of a wide range of organonitriles at 70°C. Catalyst loadings of 5mol% afford primary amide products in excellent yields in the absence of hydration-promoting additives such as oximes and hydroxylamines. Graphical abstract image
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Synthesis of spiroindenyl-2-oxindoles by montmorillonite K-10-catalyzed tandem Friedel-Crafts alkenylation/hydroarylation of propargylic alcohols with sterically hindered and electron-rich arenes ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Hwa Jung Roh, Da Young Seo, Ji Yeon Ryu, Junseong Lee, Jae Nyoung Kim Various spiroindenyl-2-oxindoles have been synthesized in a one-pot reaction from isatin-derived propargylic alcohols with sterically hindered and electron-rich arenes such as 2-phenylindole and 1,3,5-trimethoxybenzene. The reaction involved montmorillonite K-10-catalyzed tandem Friedel-Crafts alkenylation and a following hydroarylation of an allene intermediate. Graphical abstract image
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n-Butyllithium-promoted regioselective elimination of vicinal bis-triflate having an adjacent ether oxygen ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Noriki Kutsumura, Kota Shibuya, Hitoshi Yamaguchi, Takao Saito Regioselective elimination of a vicinal bis-triflate having an adjacent ether oxygen functional group has been developed. Considered in the context of our studies of the regioselective elimination of vicinal dibromide, the key to the mechanism involves the electron-withdrawing inductive effect of the neighboring oxygen functional group. Aliphatic vinyl triflate was shown to be effective in Suzuki–Miyaura cross coupling compared with corresponding aliphatic vinyl bromide. Graphical abstract image
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The intramolecular Diels-Alder vinylthiophen (IMDAV) reaction: An easy approach to thieno[2,3-f]isoindole-4-carboxylic acids ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Yuriy I. Horak, Roman Z. Lytvyn, Yevhen-Oleh V. Laba, Yuriy V. Homza, Vladimir P. Zaytsev, Maryana A. Nadirova, Tatiana V. Nikanorova, Fedor I. Zubkov, Alexey V. Varlamov, Mykola D. Obushak The reaction of readily accessible 3-(thien-2-yl)allylamines with maleic anhydride, followed by a domino sequence involving successive acylation/[4+2] cycloaddition steps, leads to the formation of the thieno[2,3-f]isoindole core. The key step, the intramolecular Diels-Alder vinylaren (IMDAV) reaction, proceeds with high level of diastereoselectivity and with formation of a single diastereoisomer of the target product 4,4a,5,6,7,7a-hexahydro-3aH-thieno[2,3-f]isoindole-4-carboxylic acids in excellent yields. If the reaction is carried out at room temperature, it occurs in 2–3days and the proton migration (H-shift) does not take place at the last stage. In boiling benzene, the reaction is complete after three hours, but in this case a slight impurity of byproducts bearing aromatic thiophene ring – 4a,5,6,7,7a,8-hexahydro-4H-thieno[2,3-f]isoindole-4-carboxylic acids is formed. Graphical abstract image
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Preparative-scale synthesis of amino coumarins through new sequential nitration and reduction protocol ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Hemchandra K. Chaudhari, Akshata Pahelkar, Balaram S. Takale In contrast to the conventional deleterious approach for nitration (for example HNO3/H2SO4) and for reduction (for example Zn/HCl), we hypothesized that sensitive heterocycles such as coumarins could not withstand with those hard conditions. Hence, while studying this reaction sequence to prepare amino coumarins (which is our ongoing project to synthesize antitubercular coumarin agents), we came across mild and greener reagent for nitration using calcium nitrate (Ca(NO3)2·4H2O; lime nitrate), and reduction using d-glucose. These two mild, chemoselective, high yielding methods are discussed herein. Graphical abstract image
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A mild halogenation of pyrazoles using sodium halide salts and Oxone ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Kathryn L. Olsen, Matthew R. Jensen, James A. MacKay A mild, inexpensive, and operationally simple pyrazole halogenation method utilizing Oxone and sodium halide salts is reported. This work documents 17 examples of alkyl, aryl, allyl, and benzyl substituted 4-chloro and 4-bromopyrazoles, obtained in up to 93% yield. Reactions are performed in water under ambient conditions and generation of organic byproducts is avoided. Graphical abstract image
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UV–vis and fluorescence detection by receptors based on an isophthalamide bearing a phenylethynyl group ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Shin-ichi Kondo, Kimihiro Endo, Jun Iioka, Keisuke Sato, Yuka Matsuta We have successfully prepared 5-(2-phenylethynyl)isophathalilc acid as a signaling unit and the corresponding derivatives for an anion receptor 2 and a barbiturate receptor 4. Receptor 2 showed characteristic UV–vis changes and dramatic fluorescence quenching upon the addition of anions and receptor 4 showed UV–vis and an OFF-ON fluorescence changes upon the addition of dibutylbarbituric acid based on the diphenylethyne moiety. Graphical abstract image
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Two new algal bromophenols from Odonthalia corymbifera ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Md. Reazul Islam, Daisuke Mikami, Hideyuki Kurihara Two new algal bromophenols, odonthalol and odonthadione, were isolated from the alga Odonthalia corymbifera. Odonthalol was determined as a trimer of brominated hydroxylated benzyl (BHB) units. Three units were connected via ether and methylene bridges. Odonthadione was identified as a hybrid compound of the BHB unit and a unique cyclopentenedione. The cyclopentenedione unit has not been reported from natural origin. Graphical abstract image
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Asymmetric synthetic approach to a functionalized azabicyclo[3.3.1]nonane moiety of (+)-sarain A ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Jiao Meng, Yu Wang, Yong Qin, Xiao-Yu Liu This paper describes our efforts toward the asymmetric synthesis of sarain A which led to efficient preparation of a functionalized azabicyclo[3.3.1]nonane moiety. The key to the synthesis relied on a base-catalyzed asymmetric Diels-Alder cycloaddition to establish multiple stereocenters of a highly substituted cyclohexenone unit and a facile intramolecular aza-Michael addition to form the desired bicyclic system. Graphical abstract image
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Copper-catalyzed regioselective allylic oxidation of olefins via C–H activation ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Nengbo Zhu, Bo Qian, Haigen Xiong, Hongli Bao A regioselective oxidation of allylic C–H bond to C–O bond catalyzed by copper (I) was developed with diacyl peroxides as oxidants. The oxidation of allylic C–H bond was accomplished with good yield and regioselectivity under mild reaction conditions. This method has a broad substrate scope including cyclic olefins, terminal and internal acyclic olefins and allyl benzene compounds. The reaction proceeds by a radical mechanism as suggested by spin trapping experiments. Graphical abstract image
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A novel HPQ-based turn-on fluorescent probe for detection of fluoride ions in living cells ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Zhou Zhao, Xinzhou Bi, Wuxiang Mao, Xiaowei Xu 2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone (HPQ) has been reported as a precipitating fluorescent molecule with excellent optical properties, such as large Stokes shift and strong fluorescence intensity. HPQF, a novel HPQ-based turn-on probe for localizable detection of fluoride ions, was designed, synthesized and fully characterized by 1H NMR, 13C NMR and HRMS. As a chemogenic fluoride probe, the tert-butyldiphenylsilane moiety of HPQF can be easily cleaved by fluoride. After spontaneous 1,6-elimination, HPQ molecule was generated to emit fluorescence under the excitation light. Further study shows that HPQF exhibited high selectivity and sensitivity for detection of fluoride. In addition, HPQF was utilized for the detection of fluoride in living cells. Graphical abstract image
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A four-step tandem synthesis of 3,5-diaroyl-4-arylpyrazoles from 1,3-diaryl-propane-1,3-diketones ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Jianlan Zhang, Wenwen Chen, Dayun Huang, Xiaobao Zeng, Xinyan Wang, Yuefei Hu A novel four-step tandem procedure was developed for efficient synthesis of 3,5-diaroyl-4-arylpyrazoles by simply stirring the mixture of 1,3-diarylpropane-1,3-diketones, TsN3, aqueous MeNH2 and Na2CO3 in DMF at 85°C for 3h. Graphical abstract image
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N-Halo succinimide-promoted one-pot three-component electrophilic cyclization: Facile access to dihalogenated heterocycles under mild conditions ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Hai-Tao Zhu, Ting-Ting Luo, Shi-Hui Shi, Ni-Ni Zhou, Si-Si Ning, Chen Zhang, Yu-Gang Xiao, Ming-Jin Fan, De-Suo Yang An effective and concise electrophilic cyclization of 1,4-butynediols, 4-aminobut-2-yn-1-ols, pent-2-yne-1,5-diols, 2-propynolphenols and 2-propynolanilines with N-halo succinimides and trimethylsilyl halides opens a one-pot synthetic access to five- and six-membered dihalogenated heterocycles in moderate to good yields. The optimized cyclization conditions are tolerated with many functional groups. Graphical abstract image
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Synthesis of bicyclopyrroles with various substituents at the bridging positions ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Satoshi Ito, Marina Tobata, Minenari Asakura, Yasutaka Shinozaki, Yuuki Iwabe, Lisa Sakamoto, Shun-pei Ito, Makoto Roppongi, Toru Oba Bicyclopyrroles are important synthetic equivalents of isoindoles, which are difficult to synthesize. Using bicyclopyrrole asa starting material, functional organic materials such as benzopyrromethene and benzoporphyrin can be synthesized. However, there are few reports on introducing substituents into bridging positions in bicyclopyrrole. By combining various reactions, we successfully obtained bicyclopyrroles with various substituents at the bridging positions. Graphical abstract image
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Synthesis of a secretoglobin 3A2 type C (98–139) fragment by Dawson’s native chemical ligation ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Mariko Kikuchi, Reiko Kurotani, Hiroyuki Konno A secretoglobin 3A2 type C (98–139) peptide was synthesized by native chemical ligation between 115Ile and 116Cys residues using Dawson’s linker. The peptide-N-acyl-benzimidazolinone-glycine amide, a C-terminal thioesters precursor, was provided from 3-amino-4-(methylamino)benzoic acid. In addition, an N-terminal cysteine fragment, the (116–139) peptide, was prepared by ordinary Fmoc-solid phase peptide synthesis. Native chemical ligation of the (98–115) fragment with the Dawson’s linker and the (116–139) peptide smoothly proceeded to give SCGB3A2 type C (98–139) peptide. Graphical abstract image
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N-Bromosuccinimide mediated synthesis of triazatruxenes from indoles ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Natthawut Toworakajohnkun, Mongkol Sukwattanasinitt, Paitoon Rashatasakhon A new synthetic method for triazatruxenes from indoles is developed using N-bromosuccinimide (NBS) as a user-friendly reagent. Major reaction parameters including the amount of NBS, substrate concentration, temperature, addition rate and addition method are investigated. Additional experiments are also conducted in order to gain access toward the reaction mechanism. Compared to the use of Br2 in the conventional method, this reaction requires less reaction time, provides better yields, and displays excellent reproducibility. The reaction can be conveniently performed at 10g scale and it is also applicable to several substituted indoles, benzoindole, and N-alkyl indoles. Graphical abstract image
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Facile benzofuran synthesis: Palladium-catalyzed carbonylative Suzuki coupling of methyl 2-(2-iodophenoxy)acetates under CO gas-free conditions ()
Publication date: 25 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 43 Author(s): Xinxin Qi, Chao Zhou, Jin-Bao Peng, Jun Ying, Xiao-Feng Wu A palladium-catalyzed carbonylative Suzuki coupling of methyl 2-(2-iodophenoxy)acetates with arylboronic acids has been developed. The reactions were performed under CO gas-free conditions and the obtained products act as a direct precursor for the synthesis of highly functionalized benzofuran derivatives. Graphical abstract image
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Editorial board ()
Publication date: 18 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 42
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Formal total synthesis of stigmatellin A ()
Publication date: 18 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 42 Author(s): J.S. Yadav, G. Revathi, B.V. Subba Reddy An efficient and stereoselective approach for the formal total synthesis of Stigmatellin A has been described. The key steps involved in this synthesis are desymmetrization of the bicyclic olefin to introduce two methyl and two hydroxyl chiral centers, Friedel Crafts acylation, regioselective demethylation, Baker-Venkataraman rearrangement and Grubbs cross metathesis. Graphical abstract image
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A concise synthesis of (+)-botryolide-E and its C-7 epimer ()
Publication date: 18 October 2017 Source:Tetrahedron Letters, Volume 58, Issue 42 Author(s): Xiaojing Liu, Ruijiao Chen, Feixia Duan, Junhao Jia, Yuqin Zhou, Xiaochuan Chen The first synthesis of (+)-botryolide-E and its C-7 epimer has been achieved in 8 steps from d-Glucono-δ-lactone, and their antibiotic activities were also investigated preliminarily. Graphical abstract image
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