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Organic Letters

Zheng-Hua Zhao, Meng-Yuan Zhang, Di-Hong Liu, Cui-Hua Zhao
The efficient synthetic route was disclosed to prepare structurally asymmetric [5]helicenes, which are substituted with either BMes2 (7B-HC) or both BMes2 and NMe2 (8B5NMe2 -HC, 7B5NMe2 -HC). Compared with the parent [5]helicene, these compounds show greatly enhanced fluorescence. In addition, they still retain fairly strong fluorescence in the solid state. Moreover, the complexation of 8B5NMe2 -HC and 7B5NMe2 -HC with fluoride can induce significant blue shift in fluorescence and the formed complexes are also highly fluorescent...
November 16, 2018: Organic Letters
Ying-Qi Zhang, Xin-Qi Zhu, Yang-Bo Chen, Tong-De Tan, Ming-Yang Yang, Long-Wu Ye
A novel Brønsted acid-catalyzed oxidative C-H functionalization of alkynyl thioethers has been developed. This method allows the practical synthesis of valuable isothiochroman-3-ones in mostly moderate to good yields under mild reaction conditions and features a broad substrate scope and wide functional group tolerance. Moreover, this metal-free oxidation can also be used to promote formal N-H insertion involving an unexpected 1,2-sulfur migration, affording useful 1,4-benzothiazin-3-ones.
November 16, 2018: Organic Letters
Pavel A Volkov, Kseniya O Khrapova, Anton A Telezhkin, Nina I Ivanova, Alexander I Albanov, Nina K Gusarova, Boris A Trofimov
Acridine adds secondary phosphine chalcogenides HP(X)R2 (X = O, S, Se; R = Ar, ArAlk) under catalyst-free conditions at 70-75 °C (both in the presence and absence of the electron-deficient acetylenes) to give 9-chalcogenophosphoryl-9,10-dihydroacridines in 61-94% yields. This contrasts with pyridines, which under similar conditions undergo an SN H Ar reaction, wherein electron-deficient acetylenes play the role of oxidants. For acridine, the SN H Ar step has been accomplished by the oxidation of the intermediate 9-phosphoryl-9,10-dihydroacridines (X = O) with chloranil...
November 16, 2018: Organic Letters
Sihan Peng, Guixia Liu, Zheng Huang
A diboration of terminal alkynes with an unsymmetrical diboron reagent pinBBdan has been achieved using LiOH as the catalyst in the presence of stoichiometric amounts of MeOH, affording 1,2-diborylalkenes with different boryl groups. The reaction proceeds in a highly regio- and stereoselective manner through cis-addition of pinBBdan to the C-C triple bond, with the Bdan moiety being incorporated at the internal position. By taking advantage of the different reactivities of the two boryl groups, the mixed diboration product can undergo the sequential, chemoselective cross-couplings with aryl bromides to form trisubstituted alkenes...
November 16, 2018: Organic Letters
Mathew L Piotrowski, Michael A Kerr
Cyclopropanation of 1,3-dienes with ethyl 2-formyldiazoacetate under rhodium catalysis results in either a tandem cyclopropanation/Cloke-Wilson rearrangement or a vinylogous variant, depending on the diene used. These adducts may be subjected to an oxygen to nitrogen substitution with various amines under palladium catalysis. The substrate scope and mechanistic reasoning is presented.
November 15, 2018: Organic Letters
Dmitry I Bugaenko, Anastasia A Dubrovina, Marina A Yurovskaya, Alexander V Karchava
A new protocol for the preparation of N-substituted indole-3-carboxylates has been developed. The key C-N bond formation occurs under transition-metal-free conditions employing a t-BuOK/DMF system without special initiators or additives. Across a number of substrates, indoles were afforded in yields higher or comparable to those obtained under transition-metal-catalyzed conditions. While demonstrating high functional group tolerance, new conditions are particularly attractive for manufacturing halogenated indoles that cannot be made in a pure form using other metal-based catalytic methods...
November 15, 2018: Organic Letters
Paolo Della Sala, Carmen Talotta, Amedeo Capobianco, Annunziata Soriente, Margherita De Rosa, Placido Neri, Carmine Gaeta
A novel hybrid host has been obtained by fusion of the calix[4]arene skeleton with a cycloparaphenylene (CPP) ring. The CPP-bridged calix[4]arene 1 combines the optoelectronic and structural properties of the CPP rings with the recognition abilities of the calix[4]arene hosts. Thus, calix-CPP 1 shows an unexpected selectivity for the Li+ cation over Na+ , as a result of more favorable cation···π interactions of Li+ with the CPP bridge and its better size complementarity.
November 15, 2018: Organic Letters
Danqing Ji, Kai Liu, Jiangtao Sun
Tandem reactions of copper-catalyzed cross-coupling of N-substituted prop-2-yn-1-amines with diazoacetates and subsequent cyclization have been developed to prepare several types of four- to six-membered heterocycles. Copper-catalyzed allenoate formation has been proven as the key step for the diverse annulations. Importantly, on the basis of the choice of different N-protecting groups of the alkyne substrates, methods toward 5,6-dihydropiperidin-2-ones, 2-methyleneazetidines, and furan derivatives have been well established...
November 15, 2018: Organic Letters
Aiyou Xia, Xin Xie, Haoyi Chen, Jidong Zhao, Chunli Zhang, Yuanhong Liu
A nickel-catalyzed cyanation of unactivated secondary alkyl chlorides or bromides using less toxic Zn(CN)2 as the cyanide source has been developed. The reaction features the use of air-stable and inexpensive NiCl2 ·6H2 O or Ni(acac)2 as the precatalysts and offers an efficient synthesis of a broad range of alkyl nitriles. Cyanation of primary alkyl chlorides or bromides was also achieved by reaction with Zn(CN)2 in the presence of n-Bu4 NCl without the need of nickel catalyst.
November 15, 2018: Organic Letters
Rei Tomifuji, Kazuki Maeda, Toshifumi Takahashi, Takuya Kurahashi, Seijiro Matsubara
The aza-Diels-Alder reaction of nonactivated dienes and imines was realized through the action of the ion-paired Lewis acid catalyst [FeCl2 ]+ [FeCl4 ]- generated by the in situ disproportionation of FeCl3 . The uniquely high reactivity of [FeCl2 ]+ [FeCl4 ]- was attributed to both the highly Lewis acidic FeCl2 + and thermodynamically stable FeCl4 - acting as an ion-paired catalyst. Synchrotron-based X-ray absorption fine structure measurements provided fundamental insights into the disproportionation and structure of the resulting ion-paired iron complex...
November 14, 2018: Organic Letters
Manas Jana, Clay S Bennett
A synthesis of the nonreducing end hexasaccharide of saccharomicin B, α-l-Eva-(1→4)-α-l-Eva-(1→4)-α-l-Dig-(1→4)-α-l-Eva-(1→4)-α-l-Dig-(1→4)-β-d-Fuc, has been developed. Selective glycosylations of l-digitoxose (l-Dig) using AgPF6 /TTBP-mediated thioether activation and l-4-e pi-vancosamine (l-Eva) using Tf2 O/DTBMP-mediated sulfoxide activation produced the hexasaccharide as a single diastereomer in very good yield. This hexasaccharide is properly functionalized to serve as a glycosyl donor for the total synthesis of saccharomicin B...
November 14, 2018: Organic Letters
Honggu Im, Dahye Kang, Soyeon Choi, Sanghoon Shin, Sungwoo Hong
Visible-light-induced intramolecular C-O bond formation was developed using 2,4,6-triphenylpyrylium tetrafluoroborate (TPT), which allows the regiocontrolled construction of cyclic ethers and lactones. The reaction is likely to proceed through the single-electron oxidation of the phenyl group, followed by the formation of a benzylic radical, thus preventing a competing 1,5-hydrogen abstraction pathway. Detailed mechanistic studies suggest that molecular oxygen is used to trap the radical intermediate to form benzyl alcohol, which undergoes cyclization...
November 14, 2018: Organic Letters
DingXi Li, Yeji Park, Jaesook Yun
A practical regioselective and diastereoselective synthesis of functionalized 1-benzo[ b]azepines by copper-catalyzed intramolecular cyclization has been developed. The reaction involves borylcupration of a mixture of ( E/ Z)-1,3-dienes, followed by capture of the generated ( Z)-allylcopper species with an imine to produce 7-membered N-heterocycles as single diastereomers. The reaction is applicable to various ( E/ Z)-dienyl arenes with an imine moiety at the ortho-position, including aryl, alkyl, and heterocyclic aldimines, and ketimines, affording borylated 2,3- cis-substituted 1-benzo[ b]azepines in good yields...
November 14, 2018: Organic Letters
Ji-Kang Jin, Feng-Lian Zhang, Qiang Zhao, Jun-An Lu, Yi-Feng Wang
A synthetic method based on radical borylation/cyclization cascades of N-allylcyanamides was developed to construct diverse boron-substituted N-heterocycles. In the reaction process, the N-heterocyclic carbene-boryl radical underwent a chemo- and regioselective addition to the alkene moiety, followed by cyclization with the N-cyano group. The resulting amide-iminyl radical intermediates underwent further reactions to afford various boron-tethered N-heterocyclic molecules. Further transformations to access synthetically useful building blocks were also demonstrated...
November 14, 2018: Organic Letters
Ananda Herath, Valentina Molteni, Shifeng Pan, Jon Loren
A versatile flow synthesis method for in situ formation of organozinc reagents and subsequent cross-coupling with aryl halides and activated carboxylic acids is reported. Formation of organozinc reagents is achieved by pumping organic halides, in the presence of ZnCl2 and LiCl, through an activated Mg-packed column under flow conditions. This method provides efficient in situ formation of aryl, primary, secondary, and tertiary alkyl organozinc reagents, which are subsequently telescoped downstream to a Negishi or decarboxylative Negishi cross-coupling reaction...
November 14, 2018: Organic Letters
Stefania De Luca, Giuseppe Digilio, Valentina Verdoliva, Michele Saviano, Valeria Menchise, Pablo Tovillas, Gonzalo Jiménez-Osés, Jesus M Peregrina
A one-pot, high-yield procedure for synthesizing lanthionine-containing peptides was developed. It relies on the S-alkylation of cysteine-containing peptides with chiral cyclic sulfamidates. The key feature of this approach is the use of mild reaction conditions (only activated molecular sieves are employed as the catalyst), leading to good chemoselectivity and excellent stereochemical control. The potential of the new methodology has been investigated by synthesizing the thioether ring of a natural lantibiotic, Haloduracin β...
November 14, 2018: Organic Letters
Bo Xu, Wen Xun, Tingzhong Wang, Fayang G Qiu
No abstract text is available yet for this article.
November 14, 2018: Organic Letters
Dan Lu, Sha Zhu, Lukasz F Sobala, Ganeko Bernardo-Seisdedos, Oscar Millet, Yongmin Zhang, Jesus Jiménez-Barbero, Gideon J Davies, Matthieu Sollogoub
Understanding the enzyme reaction mechanism can lead to the design of enzyme inhibitors. A Claisen rearrangement was used to allow conversion of an α-1,4-disaccharide into an α-1,3-linked glycosyl carbasugar to target the endo-α-mannosidase from the GH99 glycosidase family, which, unusually, is believed to act through a 1,2-anhydrosugar "epoxide" intermediate. Using NMR and X-ray crystallography, it is shown that glucosyl carbasugar α-aziridines can act as reasonably potent endo-α-mannosidase inhibitors, likely by virtue of their shape mimicry and the interactions of the aziridine nitrogen with the conserved catalytic acid/base of the enzyme active site...
November 14, 2018: Organic Letters
Kevin Yang, Alexander P Pulis, Gregory J P Perry, David J Procter
We report a transition-metal-free synthesis of benzofurans from benzothiophenes and phenols that exploits the unique reactivity of sulfoxides. Through a sequence involving an interrupted Pummerer reaction and [3,3] sigmatropic rearrangement, phenols can be combined with readily accessible yet synthetically unexplored benzothiophene S-oxides to provide C3-arylated benzofuran products. The products from this approach can undergo subsequent functionalization to gain access to a range of important benzofuran derivatives...
November 14, 2018: Organic Letters
Jian Fang, Matthias Brewer
A Lewis acid mediated intramolecular electrophilic vinylation of aryl rings by vinyl cations is reported. This reaction takes advantage of β-hydroxy-α-diazo ketones as vinyl cation precursors and provides good yields of tricyclic 1-indenones that contain a seven-membered ring. Extending the alkane chain that tethers the vinyl cation to the aromatic ring leads to 2-napthol and 2-indenone products.
November 14, 2018: Organic Letters
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