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Manuel Alcarazo, Alejandro G Barrado, Richard Goddard, Adam Zielinski
The regio- and stereoselective conversion of alkynes into (Z)-3-chloroacrylonitriles was achieved by treatment of a variety of terminal as well as internal alkynes with BCl3 in the presence of stoichiometric amounts of imidazolium thiocyanates. These products can be easily functionalized into useful building blocks, demonstrating the synthetic value of the method. Preliminary mechanistic studies suggest initial activation of the cationic thiocyanate by the Lewis acid followed by electrophilic attack of the alkyne...
August 17, 2017: Angewandte Chemie
Yang Xi, Guohao Zhu, Luning Tang, Shihan Ma, Dongming Zhang, Rong Zhang, Guangke He, Hongjun Zhu
A highly regio- and stereoselective trans-iodofluorination reaction of ynamides with NIS and Et3N·3HF has been achieved, affording (E)-α-fluoro-β-iodoenamides in moderate to good yields. The reaction proceeds under mild reaction conditions and exhibits good functional group compatibility.
August 17, 2017: Organic & Biomolecular Chemistry
Konstantin P Bryliakov
The discovery of simple and efficient catalyst systems for the asymmetric oxofunctionalization of hydrocarbons is a challenging task of catalytic chemistry. In this paper, we give an overview of catalyst systems capable of conducting asymmetric oxygenative transformations of organic molecules and, in line with the major trend to sustainability, relying on green oxidants H2O2 and O2 as the ultimate oxygen source. The full historical period of asymmetric oxidation catalysis (1970 to the present day) is covered; both transition-metal-based and organocatalytic systems are considered...
August 17, 2017: Chemical Reviews
Shao-Zhen Nie, Zhong-Yang Zhou, Ji-Ping Wang, Hui Yan, Jing-Hong Wen, Jing-Jing Ye, Yun-Yao Cui, Chang-Qiu Zhao
The secondary RP-(-)-menthyl alkylphosphine oxide was confirmed as configurationally stable toward base and was used in base-promoted alkylation, stereospecifically affording P-retained bis or functional tertiary phosphine oxides in excellent yields. The alkylated products were deoxygenated using oxalyl chloride followed by ZnCl2-NaBH4 to form P-inversed bidentate phosphine boranes in high stereoselectivities.
August 16, 2017: Journal of Organic Chemistry
Soyeong Kang, Seok Hyeon Jang, Juyeol Lee, Dong-Gil Kim, Mijin Kim, Wook Jeong, Young Ho Rhee
Catalytic asymmetric synthesis of N-heterocyclic glycosides free of protecting and directing groups is reported. The key reaction is highlighted by the atom-efficient and regioselective addition of unprotected pyrimidines to highly functionalized alkoxyallene. Numerous acyclic and cyclic N-heterocyclic glycosides are accessed with minimal formation of organic byproducts. The synthetic utility of the reaction is demonstrated by the first catalytic asymmetric synthesis of anticancer pharmaceutical (-)-Tegafur and stereoselective synthesis of an oxepane nucleoside derivative...
August 16, 2017: Organic Letters
Giorgia Casoni, Murat Kucukdisli, James M Fordham, Matthew Burns, Eddie L Myers, Varinder K Aggarwal
The stereoselective reagent-controlled homologation of boronic esters is one of a small number of iteratable synthetic transformations that if automated could form the basis of a veritable molecule-making machine. Recently, α-stannyl triisopropylbenzoates and α-sulfinyl chlorides have emerged as useful building blocks for the iterative homologation of boronic esters. However, α-stannyl benzoates need to be prepared using stoichiometric amounts of the (+)- or (-)-enantiomer of the scarcely available and expensive diamine sparteine; also, these building blocks, together with the byproducts that are generated during homologation, are perceived as being toxic...
August 16, 2017: Journal of the American Chemical Society
Li-Min Shi, Wu-Wei Dong, Hai-Yan Tao, Xiu-Qin Dong, Chun-Jiang Wang
An unprecedented asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrones with prochiral cyclopentene-1,3-diones via desymmetrization was efficiently realized with high stereoselective control with the aid of fine-tunable cinchona alkaloid derived bifunctional amine-thiourea catalysts bearing multiple hydrogen-bonding donors. This protocol provides an expedient access to the multifunctional-bridged tricyclic lactones featuring four contiguous stereogenic centers and one remote quaternary stereogenic center with a broad substrate scope...
August 16, 2017: Organic Letters
Filip Bihelovic, Desiree Stichnoth, Rolf Müller, Dirk Trauner, Frank Surup
Crocagin A (1) combines an attractive molecular structure with an unusual biosynthesis and bioactivity. Here, we present an efficient synthesis of crocagin A that hinges on an early formation of its heterotricyclic core, an electrophilic amination, and a stereoselective hydrogenation of a tetrasubstituted double bond. Our synthesis confirms the absolute configuration of crocagin A and provides access to the natural product and derivatives thereof for further biological testing.
August 15, 2017: Angewandte Chemie
Emmanuelle M D Allouche, Sylvain Taillemaud, André B Charette
Herein is described an improved synthetic route to enantio- and diastereoenriched iodocyclopropylmethanols using (diiodomethyl)zinc iodide etherate as the active species. The products obtained by this methodology were successfully functionalized by Suzuki-Miyaura cross-coupling reactions. A Buchwald-type palladium precatalyst allowed access to highly substituted and stereo-enriched cyclopropanes without requiring a protecting group.
August 15, 2017: Chemical Communications: Chem Comm
Deng-Feng Yue, Jian-Qiang Zhao, Xiao-Zhen Chen, Yan Zhou, Xiao-Mei Zhang, Xiao-Ying Xu, Wei-Cheng Yuan
A method for the enantioselective construction of hydrocarbazole skeletons through dearomative [4 + 2] annulation of 3-nitroindoles with Nazarov reagents is reported. The reactions use multiple hydrogen-bonding bifunctional thiourea as catalyst and are highly diastereo- and enantioselective (up to >20:1 dr and >99% ee). The protocol was demonstrated by preparative-scale experiment and the versatile conversion of the products. The multiple hydrogen-bonding in the catalyst plays a pivotal role in the reactivity and stereoselectivity...
August 15, 2017: Organic Letters
Christian A Malapit, Irungu K Luvaga, Donald R Caldwell, Nicholas K Schipper, Amy R Howell
A one-step preparation of 3,4-disubstituted β-lactones through Rh-catalyzed conjugate addition of aryl or alkenyl boronic acids to α-methylene-β-lactones is described. The operationally simple, stereoselective transformation provides a broad range of β-lactones from individual α-methylene-β-lactone templates. This methodology allowed for a direct, final-step C-3 diversification of nocardiolactone, an antimicrobial natural product.
August 15, 2017: Organic Letters
Sangwon Seo, Michael C Willis
A highly efficient Cu(I)-catalyzed addition/annulation sequence has been developed for the synthesis of (Z)-ylidenebutenolides employing readily available α-ketoacids and alkynes as substrates. The reactions employ a simple commercially available Cu(I)-catalyst, display good substrate scope, and deliver products with high stereoselectivity. The synthetic utility of the method is demonstrated by the straightforward derivatization of the ylidenebutenolides into a diverse range of heterocycles, and also by the preparation of the natural product bovolide, and analogs thereof...
August 15, 2017: Organic Letters
Fermín Jiménez, Antonio Fernández, Ettahir Boulifa, Ahmed Ibn Mansour, Ramon Alvarez-Manzaneda, Rachid Chahboun, Enrique Alvarez-Manzaneda
The first synthesis of antifungal sesquiterpene quinol dasyscyphin E has been achieved starting from trans-communic acid. The process described involves the first diastereoselective synthesis of this type of compound by cyclization of an aryl bicyclosesquiterpene. The acid was efficiently transformed into a sesquiterpene synthon, which was converted into the corresponding bromoaryl sesquiterpene. The key step of synthetic sequence was the cyclisation of the latter under Heck reaction conditions, which yielded the tetracyclic skeleton of the target compound with complete diastereoselectivity...
August 15, 2017: Journal of Organic Chemistry
Edmond Sanganyado, Zhijiang Lu, Qiuguo Fu, Daniel Schlenk, Jay Gan
More than 50% of pharmaceuticals in current use are chiral compounds. Enantiomers of the same pharmaceutical have identical physicochemical properties, but may exhibit differences in pharmacokinetics, pharmacodynamics and toxicity. The advancement in separation and detection methods has made it possible to analyze trace amounts of chiral compounds in environmental media. As a result, interest on chiral analysis and evaluation of stereoselectivity in environmental occurrence, phase distribution and degradation of chiral pharmaceuticals has grown substantially in recent years...
August 5, 2017: Water Research
Shanshan Liu, Gao-Wei Li, Xiao-Chao Yang, De-Yang Zhang, Min-Can Wang
A general AzePhenol dinuclear zinc catalytic system has been successfully developed and introduced into the asymmetric addition of dimethylzinc and alkynylzinc to aromatic aldehydes. In this system, an azetidine derived chiral ligand has proven to be an effective enantioselective promoter. Under the optimal reaction conditions, a series of chiral 1-hydroxyethyl (up to 99% ee) and secondary propargylic alcohols (up to 96% ee) were generated with good yields and enantioselectivities. Additionally, this novel catalytic system showed good functional group compatibility...
August 14, 2017: Organic & Biomolecular Chemistry
Rajkumar Lalji Sahani, Rai-Shung Liu
This work describes gold-catalyzed annulations of electron-deficient alkynes with benzisoxazoles to yield quinoline oxides chemoselectively. Chemical functionalizations of these resulting azacyclic compounds afforded various oxygenated tetrahydroquinolines that are present as the cores of many bioactive molecules. With the same reactants, a new relay catalysis using gold and Zn(II) catalysts affords highly oxygenated tetrahydroquinoline derivatives stereoselectively.
August 13, 2017: Angewandte Chemie
Sara Moa, Fahmi Himo
Secondary alcohol dehydrogenase from Thermoanaerobacter brockii (TbSADH) is a Zn- and NADP-dependent enzyme that catalyses the reversible transformation of secondary alcohols into ketones. It is of potential biocatalytic interest as it can be used in the synthesis of chiral alcohols by asymmetric reduction of ketones. In this paper, density functional theory calculations are employed to elucidate the origins of the enantioselectivity of TbSADH using a large model of the active site and considering two different substrates, 2-butanol and 3-hexanol...
July 24, 2017: Journal of Inorganic Biochemistry
Pellegrino La Manna, Carmen Talotta, Carmine Gaeta, Annunziata Soriente, Margherita De Rosa, Placido Neri
The threading of mono-stoppered alkylbenzylammonium axles 7+ and 8+ with the calix[6]-wheel 3 can occurs by both the routes of entering of the macrocycle 3 in the cone conformation: through-the-exo-rim and the through-the-endo-rim passage. Thus, under thermodynamic conditions, with both the axles 7+ and 8+ the two possible oriented calix[2]pseudorotaxane, namely endo-benzyl and endo-alkyl, are formed with a stereoselectivity controlled by endo-alkyl rule. Interestingly, by 1H NMR monitoring of the threading process between 8+ and 3, we revealed two calix[2]pseudorotaxane isomers in which the calix-weel adopts a 1,2,3-alternate and cone conformations, respectively, the kinetic and thermodynamic species...
August 11, 2017: Journal of Organic Chemistry
Jan-E Bäckvall, Youai Qiu, Daniels Posevins
A highly selective palladium-catalyzed allenic C-H bond oxidation was developed, which provides a novel and straightforward synthesis of [3]dendralene derivatives. A variety of [3]dendralenes with diverse substitution patterns are accessible with good efficiency and high stereoselectivity. The reaction tolerates a broad substrate scope containing various functional groups on the allene moiety, including ketone, aldehyde, ester and phenyl groups. Also, a wide range of olefins with both electron-donating and electron-withdrawing aryls, acrylate, sulfone and phosphonate groups are tolerated...
August 11, 2017: Angewandte Chemie
Romain Dubey, Robert J Comito, Zhenwei Wu, Guanghui Zhang, Adam J Rieth, Christopher H Hendon, Jeffrey T Miller, Mircea Dinca
Molecular catalysts offer tremendous advantages for stereoselective polymerization because their activity and selectivity can be optimized and understood mechanistically using the familiar tools of organometallic chemistry. Yet, this exquisite control over selectivity comes at an operational price that is generally not justifiable for the large-scale manufacture of polyfolefins. In this report we identify Co-MFU-4l, prepared by cation exchange in a metal-organic framework, as a solid catalyst for the polymerization of 1,3-butadiene with high stereoselectivity (>99 % 1,4-cis)...
August 7, 2017: Journal of the American Chemical Society
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