Tetrahedron

Editorial board ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46
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Recent advances in chemistry of ladderphanes and related polymers ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Tien-Yau Luh, Liang Ding Ladderphanes are a new type of duplex polymers. The two strands are connected by a variety of linkers via covalent bonds or hydrogen bonds. The backbones for the two polymeric strands can be symmetrical and complementary. In this Report, recent advances on the design, synthesis and properties of ladderphanes and related polymers are reviewed. Certain ladderphanes, whether symmetrical or unsymmetrical, can readily assemble on HOPG surface to exhibit highly ordered patterns. The linkers in these polymers are aligned coherently so that strong interactions between them can take place as revealed by a number of interesting photophysical properties. Graphical abstract image
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Studies on synthesis and photoreaction of tricycloundecanes endowed with β,γ-enone chromophore: Towards angular triquinanes and annulated bicyclo[4.2.0]octanes ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Raghaba Sahu, Vishwakarma Singh Cycloaddition of annulated cyclohexa-2,4-dienone with electron deficient π-partners leading to tricycloundecanes having a β,γ-enone chromophore has been reported. Studies on the photochemical reaction of the chromophoric systems upon sensitized and direct irradiation has also been presented. A highly unusual behavior of the chromophoric systems upon sensitized irradiation has also been presented. Graphical abstract image
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A simple synthesis of benzofurans by acid-catalyzed domino reaction of salicyl alcohols with N-tosylfurfurylamine ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Anton A. Merkushev, Vladimir N. Strel'nikov, Maxim G. Uchuskin, Igor V. Trushkov A simple route to polysubstituted benzofurans based on the domino reaction of commercial or easily available salicyl alcohols with N-protected furfurylamine has been designed and developed. The reaction was found to proceed with reasonable yields under heating of substrates in acetic acid in the presence of catalytic amount of conc. HCl when tosyl was used as protecting group. Graphical abstract image
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Pheromone synthesis. Part 262: Determination of the absolute configuration of the female sex pheromone [(1S,2S)-(−)-(1,2-dimethyl-3-methylenecyclopentyl) acetaldehyde] of the pineapple mealybug (Dysmicoccus brevipes) by synthesis coupled with X-ray analysis ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Kenji Mori, Jun Tabata The enantiomers of (anti-1,2-dimethyl-3-methylenecyclopentyl)acetaldehyde, one of which is the female sex pheromone of the pineapple mealybug (Dysmicoccus brevipes), were synthesized. Chirality was introduced by means of lipase-catalyzed asymmetric acetylation of (±)-2,3-dimethyl-2-cyclopenten-l-ol. X-ray analysis of (−)-camphanate ester of (1S,2S)-(−)-2-(1,2-dimethyl-3-methylenecyclopentyl)ethanol confirmed its (1S,2S)-absolute configuration. The natural pheromone was identified with the (1S,2S)-aldehyde by comparing the specific rotation, enantioselective GC retention time and pheromone activity. Graphical abstract image
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Calcium, Barium and Strontium apatites: A new generation of catalysts in the Biginelli reaction ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Sana Ben Moussa, Jalel Lachheb, Michel Gruselle, Birgit Maaten, Kadri Kriis, Tõnis Kanger, Kaia Tõnsuaadu, Béchir Badraoui We describe herein the use of Calcium, Barium and Strontium hydroxyapatites (CaHAp, BaHAp and SrHAp) as well as CaHAp containing Magnesium, Copper, Zinc and Palladium (MgHAp, CuHAp, ZnHAp and PdHAp) as catalysts in the Biginelli reaction. The efficiency of CaHAp and SrHAp is very low, leading to the expected 3,4-dihydropyrimidin-2(1H)-one in poor yields. Mixed Ba5Sr5HAp and Ba10HAp show interesting catalytic properties, especially Ba10HAp leading to pure isolated reaction products in good yields. The use of modified CaHAp seems to be of interest in regard to the yield obtained. Nevertheless the release of Mg, Cu, Zn and Pd ions in the solution during the catalytic process makes the use of such modified apatites less effective. Graphical abstract image
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Enantiospecific synthesis of antifungal dasyscyphin E from cupressic acid ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Antonio Fernández, Ettahir Boulifa, Fermín Jiménez, Soumicha Mahdjour, Ahmed I. Mansour, Rachid Chahboun, Enrique Alvarez-Manzaneda The first synthesis of the sesquiterpene quinol dasyscyphin E has been achieved starting from cupressic acid. Key steps of the synthetic sequence are the oxidative degradation of the diterpene side chain to give a methylketone, the diastereoselective α-methylation of a protected ketoaldehyde, the subsequent intramolecular aldol condensation and the further Diels-Alder cycloaddition of a dienol ester. Graphical abstract image
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Synthesis of naphthyl-substituted terminal olefins via Pd-Catalyzed one-pot coupling of acetylnaphthalene, N-Tosylhydrazide with aryl halide ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Xu Shen, Ping Liu, Yan Liu, Bin Dai In this study, a one-pot two-step Pd-catalyzed reductive eliminate between acetyl naphthalene derivatives, tosylhydrazide, and aryl halide, affording substituted 1(or 2)-(1-phenylvinyl)naphthalene in moderate-to-excellent yields, was reported. Notably, solvent played a crucial role in the coupling of 1-acetyl naphthalene derivatives (toluene) or 2-acetyl naphthalene derivatives (1, 4-dioxane) as starting materials. Meanwhile, the scope of this one-pot coupling reaction was extended to 1(or 2)-naphthaldehyde substrates. Importantly, the catalytic system can be employed on a wide variety of substrates with good functional group tolerance. This protocol could also be particularly useful for the synthesis of olefins-substituents hydroxyl compounds. Graphical abstract image
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Regioselective monobromination of aromatics via a halogen bond acceptor-donor interaction of catalytic thioamide and N-bromosuccinimide ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Pakorn Bovonsombat, Pattaradra Teecomegaet, Panisanun Kulvaranon, Aditi Pandey, Kittithorn Chobtumskul, Sireethorn Tungsirisurp, Punyanuch Sophanpanichkul, Satreerat Losuwanakul, Dechathon Soimaneewan, Patcharida Kanjanwongpaisan, Pornpawit Siricharoensang, Sirirat Choosakoonkriang Regioselective monobromination of various aromatics was achieved at room temperature using N-bromosuccinimide and 5 mol% of thioamides in acetonitrile. With thiourea as catalyst, activated aromatics, such as anisole, acetanilide, benzamide and phenol analogues containing electron donating or withdrawing groups, were brominated with high regioselectivity. Room temperature brominations of weakly activated aromatics and deactivated 9-fluorenone were accomplished by 5 mol% thioacetamide, higher substrates concentrations and longer reaction times. A backbonding of the bromine lone pairs with the π*of CS group and a halogen bond between the halogen bond donor bromine and the halogen bond acceptor sulfur of the thioamide are thought to be the principal interactions and cause of N-bromosuccinimide activation. Graphical abstract image
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Palladium-catalyzed intermolecular coupling of 2-haloallylic acetates with simple phenols, and sequential formation of benzofuran derivatives through the intramolecular cyclization ()
Publication date: 16 November 2017 Source:Tetrahedron, Volume 73, Issue 46 Author(s): Takumi Udagawa, Yukiko Tsuchi, Ikuma Takehara, Masaki Kogawa, Hirotaka Watanabe, Mitsuaki Yamamoto, Hiroaki Tsuji, Motoi Kawatsura We accomplished the synthesis of 2-substituted benzofuran derivatives by the palladium-catalyzed reaction of 2-haloallylic acetates with simple phenols in the presence of a base. The reaction proceeded through the intermolecular attack of the nucleophile on the central carbon atom of the π-allyl group, carbon-halogen bond cleavage, and sequential intramolecular cyclization. Graphical abstract image
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Editorial board ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45
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Synthesis and identification of metabolite biomarkers of 25C-NBOMe and 25I-NBOMe ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Xiongyu Wu, Caroline Eriksson, Ariane Wohlfarth, Jakob Wallgren, Robert Kronstrand, Martin Josefsson, Johan Dahlén, Peter Konradsson Synthetic routes have been developed for synthesis of potential metabolites of 25C-NBOMe and 25I-NBOMe. Nine potential metabolites have been synthesized, among which compounds 8 and 20a could be used as metabolite biomarkers of 25C-NBOMe and 20b of 25I-NBOMe in urinary detection at forensic laboratories to prove intake. Graphical abstract image
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An aryl-bridged dixanthene scaffold for building multinucleating ligands and supramolecular assemblies: Syntheses and structures ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Matthew Mudge, Alpesh Ramanlal Patel, Murat Bingül, Mohan Bhadbhade, Stephen B. Colbran An aryl-bridged dixanthene scaffold is quickly prepared and readily derivatized with functional groups at the four 4,5-positions adjacent to the oxygen atoms of the two xanthene groups: syntheses of five potentially tetradentate, multinucleating, metal-binding ligands illustrate the usefulness of the methodology. Graphical abstract image
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Strategies for the synthesis of HBGl3, a glutamic acid derived ligand bearing phenolic and azacarboxylate donor groups at the nitrogen atom ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Raminder S. Mulla, Melissa T. Walden, Dmitry S. Yufit, Tanya Desa, Elena Lurie-Luke, J.A. Gareth Williams The development of a route applicable to the preparation of acyclic glutamic acid-based chelating ligands bearing two different auxiliary donor groups linked to the nitrogen atom by methylene spacers is described and applied to the synthesis of the new polydentate ligand HBGl 3 , the first example of such a structure. The synthesis is accomplished using a strategy employing reductive amination and t-butyl ester protected intermediates. The most basic pKa values for the HBGl 3 ligand have been estimated via potentiometric and UV–Visible titration techniques. Graphical abstract image
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Janus-faced 5-methyl group in 2-hydroxy-5-methyl-[1,4]-benzoquinone ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Thomas Rosenau, Nele Sophie Zwirchmayr, Takashi Hosoya, Andreas Hofinger-Horvath, Markus Bacher, Antje Potthast The 5-methyl group in 2-hydroxy-[1,4]-benzoquinone shows a peculiar reactivity that depends on the pH of the reaction medium. Under acidic conditions, ortho-quinone methide tautomers of the parent para-quinones are present in equilibrium. The 5-methylene group is stabilized by resonance, incorporating canonic structures with a positive charge at this position and now acting as carbenium equivalent. These ortho-quinone methide intermediates can be trapped in hetero-Diels-Alder reactions with inverse electron demand or by reaction with trimethylsilyl chloride. Under alkaline/basic conditions, the 5-methyl group is deprotonated, this time performing as carbanion equivalent being once more stabilized by resonance. This facet of reactivity was used for instance in regioselective perdeuteration of the 5-methyl position or in Michael additions. The reaction medium is thus able to govern the chemical behavior of the 5-methyl group, to effect its umpoling and to switch the reactivity to the opposite. Like the Roman god Janus, these methyl groups have two faces, and the reaction medium decides which one is presented. Graphical abstract image
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[Cu(maloNHC)]-catalyzed synthesis of 2-aryl pyrazolo[5,1-a]isoquinolines by annulation of N′-(2-((trimethylsilyl)ethynyl)benzylidene)hydrazides with terminal aromatic alkynes ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Huixin Liu, Le Lu, Ruimao Hua A [Cu(maloNHC)]-catalyzed synthesis of 2-aryl pyrazolo[5,1-a]isoquinolines via annulation of N′-(2-((trimethylsilyl)ethynyl)benzylidene)hydrazides with terminal aromatic alkynes was developed. Graphical abstract image
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Synthesis of tricyclic units of indole alkaloids: Application of Fischer indolization and olefin metathesis ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Sambasivarao Kotha, Vikas R. Aswar, Gaurav Singhal Simple synthetic approaches to pyridocarbazole and azepinocarbazole derivatives have been reported via Fischer indolization, Grignard reaction and olefin metathesis as key steps. In addition, a combination Sonogashira coupling and Pauson-Khand reaction has been used to assemble extended pyridocarbazole derivative. Graphical abstract image
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Chiron approach for the total synthesis of (+)-synargentolide B ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Jun Liu, Yangguang Gao, Linlin Wang, Yuguo Du A concise and efficient chiron approach for the total synthesis of natural product synargentolide B was achieved in 10 steps with overall yields of 11.3% from D-mannitol and L-ethyl lactate. The key reactions included anti-Barbier allylation, cross-metathesis, and an intramolecular Yamaguchi esterification. Graphical abstract image
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Synthesis of 1,10-seco-triterpenoids by the Beckmann fragmentation from allobetulin ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Irina A. Tolmacheva, Alexey V. Nazarov, Maxim V. Dmitriev, Eugene I. Boreko, Victoria V. Grishko A new convenient route to synthesize 1,10-seco-triterpenoids from allobetulin was demonstrated. Stereoisomerism of starting oleanane 1-oximes was determined by X-ray crystallography and additionally confirmed by the structure of the obtained Beckmann rearrangement products. Absolute configuration of chiral centers of 1,10-secotriterpenoids was found to be identical to that of stereocenters in respective precursors. Antiviral activity of 1,10-seco-derivatives was studied against herpes simplex virus type I. Graphical abstract image
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Highly regioselective synthesis of 2,3-disubstituted 2H-1-benzopyrans: Brønsted acid catalyzed [4+2] cycloaddition reaction with a variety of arylalkynes via ortho-quinone methides ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Kenta Tanaka, Mayumi Sukekawa, Yosuke Shigematsu, Yujiro Hoshino, Kiyoshi Honda A highly regioselective one-pot synthesis of 2,3-disubstituted-2H-1-benzopyrans has been developed through Brønsted acid catalyzed [4+2] cycloaddition reaction with a variety of arylalkynes via ortho-quinone methides. A catalytic amount of trifluoromethanesulfonic acid effectively promotes the [4+2] cycloaddition reaction of salicylaldehydes with arylalkynes to afford the corresponding 2H-1-benzopyrans in good yields with high regioselectivities. Treatment of the cycloadduct 2,3-diphenyl-2H-1-benzopyran with some nucleophiles led to 4H-1-benzpyrans and 2H-1-benzopyran according to reagents. The present reactions provide versatile access to functionalized 2,3-disubstituted-2H-1-benzopyrans that would be a useful tool for the synthesis of biologically and photochemically active molecules. Graphical abstract image
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Sulfonylative alkoxyhydroxylation of 2-arylpropenes ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Huei-Sin Wang, Yan-Shin Wu, Meng-Yang Chang One-pot three-step sulfonylative alkoxyhydroxylation of 2-arylpropenes 1 affords oxygenated sulfonylcumenes 4 in moderate yields via a sequential route: (i) NBS-mediated allylic bromination of 2-arylpropenes 1 in CH2Cl2, (ii) sodium sulfinates 2-promoted nucleophilic substitution of the resulting styryl bromides in a co-solvent of alcohol and water, and (iii) V2O5/H2O2 mediated alkoxyhydroxylation of corresponding styryl sulfones 3 in alcohol. The synthetic route provides a highly effective protocol for the 1,2,3-tricarbofunctionalization of 2-arylpropenes 1 via two carbon-oxygen and one carbon-sulfur bond formations. Graphical abstract image
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Rose Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Ling-Ling Wu, Li Tang, Shui-Gen Zhou, Yi-Jie Peng, Xiao-Dong He, Zhi Guan, Yan-Hong He We report an example of Rose Bengal-photosensitized oxidation of tertiary amines for the synthesis of bis-1,3-dicarbonyl compounds. This protocol employs Rose Bengal as a visible-light absorbing photocatalyst without the need of a transition metal, and air as a green oxidant. Various functional groups were well tolerated to afford products with yields of up to 80% under mild reaction conditions. Graphical abstract image
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Effects of aromatic stabilization energies of aryl rings of symmetrical diarylethenes ()
Publication date: 9 November 2017 Source:Tetrahedron, Volume 73, Issue 45 Author(s): Huitao Xu, Shasha Wei, Congbin Fan, Gang Liu, Shouzhi Pu Four symmetrical diarylethenes bearing a variable aryl unit were synthesized and their crystal structures and photochromic performances were systematically studied to elucidate the effects of the aromatic stabilization energy (ASE) of aryl units. Experimental results revealed strong correlations of the thermal stability, as well as cyclization quantum yield, photoconversion ratio, and molar absorption coefficient of the darylethenes with the ASE of aryl units. Graphical abstract image
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Editorial board ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44
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Progress in the total synthesis of epoxyquinone natural products: An update ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Goverdhan Mehta, Saumitra Sengupta Epoxyquinone natural products continue to attract the attention of organic synthesis community worldwide, owing to their increasingly diverse and complex molecular architectures and broad spectrum biological activities associated with them. The last decade, in particular, has witnessed considerable activity and advances towards the total synthesis of this family of natural products with some notable successes. These efforts, deploying appropriate, contextual and emergent synthetic methodologies have led to the total synthesis of numerous epoxyquinone natural products spread over the entire structural landscape, with the added value of generating new chemical diversity space around their scaffold. This flurry of activity since 2005 lends some urgency to provide an update that documents and highlights the achievements in the intervening years and reflects on the new opportunities and challenges that lie ahead. Graphical abstract image
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SET-promoted photoaddition reactions of fullerene C60 with tertiary N-trimethylsilylmethyl substituted α-aminonitriles. Approach to the synthesis of fulleropyrrolidine nitriles ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Suk Hyun Lim, Dae Won Cho, Jungkweon Choi, Hyunjun An, Jun Ho Shim, Patrick S. Mariano Photoaddition reactions of C60 with tertiary N-arylmethyl-N-trimethylsilylmethyl substituted α-aminonitriles were explored. The results show that these photoreactions produce both trimethylsilyl- and cyano group containing fulleropyrrolidines as major products through pathways involving 1,3-dipolar cycloaddition of azomethine ylide intermediates. The ylides are formed either by SET from α-aminonitriles to the triplet excited state of C60 (in N2-purged solutions) followed by desilylation or deprotonation, or by hydrogen atom abstraction by singlet oxygen (in O2-purged solutions). In contrast, photoreactions of C60 with analogous amines that do not contain trimethylsilyl group form fulleropyrrolidines that contain aryl- and cyano substitutents on the pyrrolidine ring. The efficiencies of these photoaddition reactions are influenced by several factors including reaction condition (N2 or O2-purged), solvent polarity, the electronic and structural nature of α-aminonitriles and additive. The presence of trimethylsilyl group in the α-aminonitrile substrates plays a crucial role in enhancing the efficiencies of the fulleropyrrolidine forming reactions. Graphical abstract image
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Neuroprotective phenylethanoid glycosides with dioxane units from the fruits of Forsythia suspensa ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Si-Yuan Shao, Fan Zhang, Zi-Ming Feng, Ya-Nan Yang, Jian-Shuang Jiang, Pei-Cheng Zhang Six new phenylethanoid glycosides possessing dioxane moieties, named forsyoxasides A−F (1–6), together with four known such compounds (7–10) were isolated from the fruits of Forsythia suspensa. These structures were illustrated by extensive NMR spectroscopic techniques and by comparing their NMR data with the related literatures. Notably, forsyoxaside A (1) is a novel dioxane phenylethanoid glycoside with an axial aromatic ring, which is rare in the natural sources. Compounds 1, 4, 7 and 8 showed remarkable bioactivities against rotenone induced PC12 cell damage. Furthermore, 1 and 7 displayed strong activities against serum deprivation induced damage on the same cells. Graphical abstract image
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Synthesis of novel 4-ferrocenyl-1,2,3,4-tetrahydroquinolines and 4-ferrocenylquinolines via α-ferrocenyl carbenium ions as key intermediates ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Aleksandra Minić, Dragana Stevanović, Mirjana Vukićević, Goran A. Bogdanović, Matthias D'hooghe, Niko S. Radulović, Rastko D. Vukićević A series of novel 4-ferrocenyl-1,2,3,4-tetrahydroquinolines were synthesized in high-to-excellent yields (up to 99%) starting from the corresponding ferrocenoylethyl aryl amines. These Mannich bases were reduced (NaBH4) to the corresponding 3-(arylamino)-1-ferrocenylpropan-1-ols and submitted to an intramolecular cyclization prompted by acetic acid, proceeding via the corresponding α-ferrocenyl carbenium ion intermediates. Subsequently, the obtained tetrahydroquinolines were smoothly oxidized (aromatized) by means of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to provide the corresponding 4-ferrocenylquinolines (up to 93%). Graphical abstract image
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The value of 2JP–CO as a diagnostic parameter for the structure and thermal reactivity of carbonyl-stabilised phosphonium ylides ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): R. Alan Aitken, Youcef Boubalouta, Da Chang, Lee P. Cleghorn, Ian P. Gray, Nazira Karodia, Euan J. Reid, Alexandra M.Z. Slawin A survey of 20 carbonyl-stabilised phosphonium ylides with recently reported X-ray structures shows a strong correlation between the CP to CO torsion angle and the value of 2 J P–CO, with high values being associated with an anti configuration and low with syn. Seven new X-ray structural determinations are reported, several for types of ylide not crystallographically characterised before, and these also conform to this pattern. The value of 2 J P–CO is then correlated with whether or not thermal extrusion of Ph3PO occurs to give alkynes for over 200 ylides and an empirical rule developed that the extrusion never occurs for ylides where this value is > 11 Hz. This is used to rationalise the anomalous behaviour of some trioxo ylides and cyclic ylides, two of which afford cycloalkynes, isolated after rearrangement as the isomeric 1,3-dienes. The rule also holds for a family of novel highly fluorinated ylides which afford fluorinated alkynes in good yield upon flash vacuum pyrolysis. Graphical abstract image
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The relevance of the relative configuration in the folding of hybrid peptides containing β-cyclobutane amino acids and γ-amino-l-proline residues ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Ona Illa, José Antonio Olivares, Pau Nolis, Rosa M. Ortuño Four new series of diastereomeric β,γ-di- and β,γ-tetrapeptides derived from conveniently protected (1R,2S)- and (1S,2S)-2-aminocyclobutane-1-carboxylic acid and cis- and trans-γ-amino-l-proline joined in alternation have been synthesized. High resolution NMR experiments show that peptides containing trans-cyclobutane amino acid residues adopt a more folded structure in solution than those containing a cis-cyclobutane residue, which adopt a strand-like structure. The cis/trans relative configuration of the cyclobutane residue is the origin of the folding pattern of each peptide due to either intra- or inter-residue hydrogen-bonded ring formation, whereas the cis/trans isomerism of the γ-amino-l-proline residue does not have a significantly relevant role on the folding ability of these peptides. Graphical abstract image
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Mitsunobu C-alkylation of β-alkoxycarbonyl 2-nitrobenzenesulfones and its use for the rapid synthesis of novel benzothiazine derivatives ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Martina Drábiková, Soňa Krajčovičová, Miroslav Soural Herein, we report the first examples of the Mitsunobu alkylation of β-alkoxycarbonyl 2-nitrobenzenesulfones. Wang resin was acylated with α-halocarboxylic acids followed by the reaction with 2-nitrothiophenols. After oxidation with m-chloroperbenzoic acid, the immobilized β-alkoxycarbonyl 2-nitrobenzensulfones were subjected to alkylation with various alcohols. The reaction outcome strongly depended on the selection of the alkylating species. After the reduction of the nitro group, acid-mediated cleavage and subsequent cyclization, the C2-(di)substituted benzothiazin-3(4H)-one 1,1-dioxides were obtained in high crude purities and good overall yields. Graphical abstract image
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Asymmetric double donor-π-acceptor dyes based on phenothiazine and carbazole donors for dye-sensitized solar cells ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Bo-ye Zhu, Liang Wu, Qin Ye, Jian-rong Gao, Liang Han Four organic dyes with asymmetric double donor-π-acceptor system were designed, synthesized and utilized in dye-sensitized solar cells (DSSCs), where phenothiazine and carbazole were introduced as double donors, butyl or octyl chain as the linker and cyanoacetic acid or rhodanine acetic acid as the electron acceptor. The design of double donor-π-acceptor system contributes to a distinctive increase of the molar extinction coefficient and benefits light-harvesting capability of these dyes. Due to superior electron injection efficiency, CPC-series dyes with cyanoacetic acid acceptor exhibit broader IPCE spectra and high IPCE responsive value compared with rhodanine-3-acetic acid acceptor, leading to higher J SC . Long alkyl chain favors antiaggregation effect and low charge recombination rate is observed for dyes with octyl chain which display higher V OC than those with butyl chain. Among four dyes, dye with octyl chain and cyanoacetic acid acceptor exhibits the highest short-circuit photocurrent density (9.64 mA cm−2) and open-circuit photovoltage (720 mV), leading to the best overall power conversion efficiency of 4.76%. Graphical abstract image
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Unusual visible-light photolytic cleavage of tertiary amides during the synthesis of cyclolignans related to podophyllotoxin ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Kamil Lisiecki, Krzysztof K. Krawczyk, Piotr Roszkowski, Jan K. Maurin, Armand Budzianowski, Zbigniew Czarnocki During the attempted photochemical cyclization of 2,3-bisbenzylidene-γ-hydroxybutyric acid cyclic amide ester, it was observed that a γ-butyrolactone ring was formed, which was concurrent with the release of the amine fragment from the amide. The process occurs with high yield giving rise to the formation of β-apopicropodophyllin and its regioisomer. Additional experiments confirmed the photochemical nature of this transformation, and that it is independent from the photocyclization of the benzylidene groups – a typical reactivity for the members of the fulgide family. In contrast to the latter UV-driven cyclization, the photochemical cleavage of the amide was proven to proceed under irradiation with visible light. Graphical abstract image
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Expanding the scope of methyl xanthate esters - From Barton-McCombie reaction auxiliary to versatile protective group ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Karin Thorsheim, Sophie Manner, Ulf Ellervik The methyl xanthate ester is presented as a versatile protective group for alcohols. Hydroxyl groups can easily be transformed into methyl xanthate esters by several methods and are commonly used as an auxiliary in the Barton-McCombie reaction. We show that these methyl xanthate esters can readily and chemoselectively be cleaved under mild conditions by the action of diethylenetriamine using microwave heating. This method is orthogonal to many common hydroxyl protective groups that can be introduced and cleaved in the presence of methyl xanthate ester. Graphical abstract image
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Mechanism of С-Н cyclization of alkynylanthraquinones into thienoanthraquinones with the participation of sodium sulfide ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Lidiya Fedenok, Fedor Dultsev, Igor Barabanov, Nikolay Polyakov The CH-cyclization of alkynyl-9,10-anthraquinones 1 into thienoanthraquinones 2 is shown to be initiated by the neutral S2 molecule and not by the sulfide anion as it is assumed in the existing model of CH-cyclization with the nucleophiolic substitution of H. The formation of S2 takes place in the reaction medium due to the partial reduction of the substrate 1 by Na2S into the corresponding anthrahydroquinone, which is inactive in the main reaction. We present a new cyclization mechanism with the key stage involving the electrophilic displacement of H, which results in the formation of the reaction product 2 and elimination of S. In the reaction medium atomic sulfur is transformed into S2, which initiates the next cyclization act. This determines the chain nature of cyclization with the participation of S2. Within this model, the route to increase the yield of target thienoanthraquinones is proposed through the introduction of a neutral quinone able to generate S2 by means of easy reduction. Graphical abstract image
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Diels-Alder reactions of fused 5-, 6- and 7-membered ring 2-vinylindoles: Synthesis of annulated tetrahydrocarbazoles ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Wayland E. Noland, Ryan J. Herzig, Honnaiah Vijay Kumar, Venkata Srinivasarao Narina, Pavel K. Elkin, Karen I. Valverde, Briana L. Kim Scaffolds of tetrahydrocarbazoles are an important class of biologically active compounds found abundant in nature. In the present investigation, functionalized polycyclic tetrahydrocarbazoles were synthesized using Diels-Alder cycloaddition between fused 5-, 6- and 7-membered ring 2-vinylindoles and various dienophiles. The dienophiles used were N-phenylmaleimides, 1,4-naphthoquinone, and dimethyl acetylenedicarboxylate (DMAD). When 1,4-naphthoquinone was used as a dienophile, the 5-membered ring Diels-Alder adduct was obtained in the oxidized form, but this form was not observed in the case of 6- and 7-membered ring Diels-Alder adducts. The desired product yields ranged from 60–70% and the structure of final compounds were determined using 1D and 2D NMR analysis. 1H NMR studies confirmed excellent diastereoselectivity (>99% de). Graphical abstract image
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Convenient two-step synthesis of highly functionalized benzo-fused 1,4-diazepin-3-ones and 1,5-diazocin-4-ones by sequential Ugi and intramolecular SNAr reactions ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Simon Vézina-Dawod, Nicolas Gerber, Xinxia Liang, Eric Biron Benzodiazepinones are an important family of heterocycles with very attractive pharmacological properties and peptidomimetic abilities. We report herein a rapid and efficient two-step synthesis of polysubstituted 1,4-benzodiazepin-3-ones and 1,5-benzodiazocin-4-ones using a multicomponent condensation/cyclization strategy. The approach uses an Ugi four-component reaction to condense readily available N α -Fmoc-amino acids, amines and isocyanides with a 2-fluorobenzaldehyde derivative followed by a one-pot Fmoc-group removal, intramolecular aromatic nucleophilic substitution for ring closure and side chain deprotection. The described method gives access to benzo-fused 7- and 8-membered rings bearing a wide variety of functionalized substituents and was applied to efficiently prepare tri- and tetrasubstituted 1,4-benzodiazepin-3-ones and 1,5-benzodiazocin-4-ones in high yields in two straightforward steps. Graphical abstract image
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2′-Aminoanalogues of the cruciferous phytoalexins spirobrassinin, 1-methoxyspirobrassinin and 1-methoxyspirobrassinol methyl ether: Synthesis and anticancer properties ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Mariana Budovská, Viera Tischlerová, Ján Mojžiš, Marianna Harvanová, Oleksandr Kozlov, Taťána Gondová, Nataša Tomášková A method for the synthesis of new 2′-aminoanalogues of spiroindoline phytoalexins is reported. 2′-Aminonalogues of spirobrassinin, 1-methoxyspirobrassinin and 2,2′-diamino analogues of 1-methoxyspirobrassinol methyl ether were prepared by substitution of the methylsulphanyl group on the dihydrothiazole ring of corresponding phytoalexins. Final products were obtained by heating the phytoalexins with aniline or substituted aniline in the absence of solvent at 120 or 140 °C. By replacement of the SCH3 moiety of (S)-(−)- or (R)-(+)-spirobrassinin, enantiomers of 2′-aminoanalogues of spirobrassinin were also synthesized. Determination of their enantiomeric compositions using HPLC with chiral stationary phase revealed partial enantiomeric enrichment. The occurence of a SIDA effect of our 2′-aminonalogue of spirobrassinin was evaluated by examination of a non-racemic mixture in non-polar C6D6. Complete enantioresolution and distinct signals for two enantiomers were observed for a number of 1H and 13C NMR resonances. New synthesized compounds were supplied for testing the antiproliferative effect on a panel of six human cancer cell lines. 2′-Aminoanalogue with CF3 functionality exhibited more significant inhibitory effects than natural phytoalexins spirobrassinin. Graphical abstract image
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Diversity-oriented synthesis of 1,3-benzodiazepines ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Gaigai Wang, Chao Liu, Binbin Li, Yingchun Wang, Kristof Van Hecke, Erik V. Van der Eycken, Olga P. Pereshivko, Vsevolod A. Peshkov A concise assembly of the 1,3-benzodiazepine core from A3-coupling-derived propargylamines and ortho-bromophenylisocyanates is described. The developed synthetic sequence involves the addition of propargylamine to isocyanate followed by palladium-catalyzed intramolecular alkyne hydroarylation that could be accomplished in a stepwise or one-pot manner. Graphical abstract image
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Synthesis of the AE bicyclic of Daphniphyllum alkaloid yuzurine ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Yue Meng Liu, Fei Li, Qi Wang, Jun Yang A concise synthesis of the AE bicyclic system of Daphniphyllum alkaloid yuzurine is described. The synthetic sequence features a Dieckmann condensation to construct ring A, reduction of α, β-unsaturated double bond and propargylation of α-position of lactone to diastereoselectively generate relative stereocenter C-3, C-4 and C-5, and an acid-catalyzed cyclization to assemble ring E. Graphical abstract image
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Self-recognition behavior of novel frameworks containing both urea and carboxylate anion motifs ()
Publication date: 2 November 2017 Source:Tetrahedron, Volume 73, Issue 44 Author(s): Zhiqiang Xu, Haojie Ge, Xie Han, Sheng Hua Liu, Xiang-Gao Meng, Jun Yin Molecular recognition based on hydrogen bond interaction plays a significant role in supramolecular self-assembly. In this work, we successfully developed a class of novel frameworks containing a urea in the recognition site and a carboxylate anion in the guest unit. The self-recognition model based on the interaction between urea and carboxylate anion could induce the molecules to assemble into a highly organized form. The crystal structures showed that they assembled in highly ordered two-dimensional architectures. The optical properties showed that the position of carboxylate anion on the diphenylacetylene backbone had an obvious influence on optical properties. The self-recognition strategy is useful for the construction of highly ordered self-assembled architectures. Graphical abstract image
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Editorial board ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43
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Reactions of tetracyclic γ-sultones with N-nucleophiles. Novel synthesis of 3,4-disubstituted homoadamantanes ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Marat R. Baimuratov, Marina V. Leonova, Vadim A. Shiryaev, Yuri N. Klimochkin Derivatives of (homo)adamantane sulfonic acids are synthesized through the reaction of tetracyclic γ-sultones with ammonia and hydrazine hydrate. In the presence of a strong base and prolonged heating the reactions of γ-sultones with ammonia or hydrazine hydrate occur through CO cleavage and lead to products with a modified carbon skeleton. Ring opening of trans-γ-sultones proceeds with inversion of configuration of the carbon atom linked to sulfur. The reaction of bromomethyl sultones with secondary amines proceeds through dehydrohalogenation and leads to products of Michael addition. Graphical abstract image
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Synthesis of five-membered unsaturated compounds from ketones via cyanophosphates under neutral conditions: [1,5]-CH insertion of alkylidene carbenes generated by tetrazole fragmentation ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Hiroki Yoneyama, Kenji Uemura, Yoshihide Usami, Shinya Harusawa Cyanophosphates (CPs) can easily be prepared via the reactions of carbonyl compounds with diethyl phosphorocyanidate (DEPC) in the presence of LiCN (cat.) under non-aqueous conditions. Treatment of ketone-derived CPs with TMSN3/Bu2SnO (cat.) in toluene at reflux produces cyclopentenes or heterocyclic products in good yields under neutral conditions. In this two-step transformation, CPs may form tetrazolylphosphates, which subsequently undergo successive fragmentation to generate alkylidene carbenes, which undergo [1,5]-C–H insertions to yield five membered compounds. Graphical abstract image
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Steric buttressing in the Pauson-Khand reactions of benzyl enynes ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Christian E. Madu, H.V. Rasika Dias, Carl J. Lovely The application of the intramolecular Pauson-Khand reaction of 1,n-enynes provides a convenient method for the construction of polycyclic frameworks but this process has largely been limited to the formation of 5,5- and 5,6-fused ring systems. In this report, we describe the application of the Pauson-Khand cyclization to 1,8-enynes embedded in an aromatic ring system wherein it is determined that the presence of steric buttresses in the form of t-butyl groups facilitates the cycloaddition. These reactions proceed in good yields with either thermal or oxidative activation and in the former case, the diastereoselectivities are high. An investigation of the tolerance of this cycloaddition to substitution around the 1,8-enyne demonstrates that only 2,2-disubstitution does not result in productive cyclization. Cycloadditions with hydroxyl groups at the propargylic position while leading to fused rings are compromised by side reactions leading to reduction and in some cases tautomerization. However, these byproducts are easily minimized through conversion of the hydroxyl group to the corresponding silyl ether. Graphical abstract image
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CS and CN bond formation via Mn-promoted oxidative cascade reaction: Synthesis of C3-sulfenated indoles ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Lin He, Xianwei Li Thioethers are of synthetic value in pharmaceutical molecules and nature products, herein, we report an oxidative cascade reaction that delivers multiple substituted indole thioethers with great efficiency. This transformation utilized ortho-azido aromatic alkynes as the substrates, and sulfonyl hydrazides as the sulfenation reagent promoted by Mn(III) catalyst. Notably, great functional group tolerance, in combination with nitrogen and water as the byproducts, highlighted the sustainable chemistry of this protocol. Graphical abstract image
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Diversity-oriented synthesis of cyclopropyl peptides from Ugi-derived dehydroalanines ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): David A. Contreras-Cruz, Miguel A. Sánchez-Carmona, Fabio A. Vengoechea-Gómez, Daniel Peña-Ortíz, Luis D. Miranda A three-step synthesis of cyclopropyl peptides is reported. The protocol involves a consecutive Ugi-4CR/elimination reaction to prepare dehydroalanines followed by a Corey-Chaykovsky cyclopropanation reaction. Peptide-like molecules that resemble some pharmacologically active compounds with a variety of substituents in the cyclopropane ring were prepared. When (2-ethoxy-2-oxoethyl) dimethyl sulfonium ylide was used the reaction exclusively gives the cis-diastereoisomer cyclopropanes in good yields from readily prepared starting materials. A collection of 26 highly substituted cyclopropyl peptides were obtained. Graphical abstract image
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Synthesis and anti-proliferative activity of 3′-deoxy-3′-fluoro-3′-C-hydroxymethyl-pyrimidine and purine nucleosides ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Naresh Bhuma, Sachin S. Burade, Aditi V. Bagade, Navanath M. Kumbhar, Kisan M. Kodam, Dilip D. Dhavale A new class of 3′-deoxy-3β′-fluoro-3α′-C-hydroxymethyl-pyrimidine 1a-c and purine 1d nucleosides were synthesized using modified Corey-Link reaction with 3-oxo-d-glucofuranose derivative to get C-3 quaternary carbon with 3β′-fluoro-3α′-C-hydroxymethyl groups, in the sugar frame work. Conformational preferences of fluorinated nucleosides were studied by the DFT calculations. Anti-proliferative activity of nucleosides 1a-d was tested against MDA-MB-231, L-132, HeLa and neural cell lines and found to be moderate active. Graphical abstract image
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A multiple switching diarylethene dimer with a bis(benzylene)amine-linked naphthalimide unit ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Shasha Wei, Xue Li, Congbin Fan, Gang Liu, Shouzhi Pu A novel photochromic diarylethene dimer with a bis(benzylene)amine-linked naphthalimide unit was synthesized, and its photochemical properties were systematically studied. Upon irradiation with ultraviolet light, a singly-closed isomer and a fully-closed isomer were reversibly formed, which were confirmed by the results of Nuclear Magnetic Resonance spectroscopy (NMR) and High-Performance Liquid Chromatography (HPLC). Additionally, the diarylethene dimer could be used as a multi-addressable fluorescence switch when triggered by light, proton, and metal ions. Moreover, a logic circuit was constructed with the unimolecular platform by using the fluorescence intensity at 445 nm as output and appropriate combinational stimuli of UV light, Al3+, and EDTA as inputs. Graphical abstract image
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Syntheses of two kinds of disaccharide subunits of antitumor antibiotic bleomycins ()
Publication date: 26 October 2017 Source:Tetrahedron, Volume 73, Issue 43 Author(s): Rui Che, Qiwen Zhu, Jie Yu, Jiao Li, Jiahui Yu, Wei Lu Gram-scale syntheses of two kinds of bleomycin disaccharides are described. l-gulose subunit 12 was accomplished with a novel and short route in six steps and 37% overall yield from 4, which could be easily prepared from the commercially available inexpensive material d-sorbitol, while 6-deoxy-l-gulose subunit was synthesized in 11 steps in 8% yield from d-glucolactone. The disaccharides were then prepared in a previously reported glycosidation coupling of the 3-O-carbamoyl-mannosyl donor with the l-gulopyranoside acceptors. Both disaccharides were finally obtained in gram-scale and the total synthesis of disaccharide 2 was achieved the first time. Graphical abstract image
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