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https://www.readbyqxmd.com/read/28525685/asymmetric-synthesis-of-secondary-and-tertiary-boronic-esters
#1
Varinder Kumar Aggarwal, Beatrice Collins, Claire Wilson, Eddie Myers
Non-racemic chiral boronic esters are recognised as immensely valuable building blocks in modern organic synthesis. Their stereospecific transformation into a variety of functional group - from amines and halides to arenes and alkynes - along with their air and moisture stability, has established them as an important target for asymmetric synthesis. Efforts towards the stereoselective synthesis of secondary and tertiary alkyl boronic esters have spanned over five decades and are underpinned by a wealth of reactivity platforms, drawing on the unique and varied reactivity of boron...
May 18, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28524077/highly-stereoselective-synthesis-of-a-compound-collection-based-on-the-bicyclic-scaffolds-of-natural-products
#2
Murali Annamalai, Stanimira Hristeva, Martyna Bielska, Raquel Ortega, Kamal Kumar
Despite the great contribution of natural products in the history of successful drug discovery, there are significant limitations that persuade the pharmaceutical industry to evade natural products in drug discovery research. The extreme scarcity as well as structural complexity of natural products renders their practical synthetic access and further modifications extremely challenging. Although other alternative technologies, particularly combinatorial chemistry, were embraced by the pharmaceutical industry to get quick access to a large number of small molecules with simple frameworks that often lack three-dimensional complexity, hardly any success was achieved in the discovery of lead molecules...
May 18, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28523904/enantioselective-propargylation-of-polyols-and-desymmetrization-of-meso-1-2-diols-by-copper-borinic-acid-dual-catalysis
#3
Ren-Zhe Li, Hua Tang, Ke R Yang, Li-Qiang Wan, Xia Zhang, Jie Liu, Zhengyan Fu, Dawen Niu
A copper/borinic acid dual catalytic reaction enabled the enantioselective propargylation of aliphatic polyols. Readily available reagents and catalysts were used in this transformation, which displayed good to excellent chemo- and stereoselectivity for a broad array of substrates. The method was also applicable to the desymmetrization of meso 1,2-diols to furnish products with three stereogenic centers and a terminal alkyne group in one operation.
May 19, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28523728/lewis-base-mediated-silylations-of-alcohols-asymmetric-synthesis-of-chiral-organosilicon-compounds-controlled-by-chiral-ar-binmols
#4
Li-Wen Xu
In the past years, successful stereoselective functionalizations of hydroxyl groups of alcohol substrates with chlorosilanes have evolved silyl ether formation from a functional group protection to an enantioselective synthetic strategy. In this work, a family of structurally specific chiral diols, chiral 1,1'-binaphthalene-2--arylmethanol-2'-ol (Ar-BINMOL), -controlled desymmetrization of dichlorosilanes is presented, which led to the facile construction of desired silicon-stereogenic organosilicon compounds with high yields and good diastereoselectivities...
May 18, 2017: Chemistry, An Asian Journal
https://www.readbyqxmd.com/read/28521074/metal-free-hydroalkoxylation-formal-4-2-cycloaddition-cascade-for-the-synthesis-of-ketals
#5
Santosh J Gharpure, Santosh Kumar Nanda, Padmaja Padmaja, Yogesh Gangaram Shelke
A transition metal free, acid promoted cascade hydroalkoxylation-formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano-chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo-dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an exo-dig fashion leading to spiroketals. The study revealed that intramolecular hydroalkoxylation of alkynols is a preferred path over a generation of oxocarbenium ion formation when coupling partner is salicylaldehyde...
May 18, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28517935/regio-and-stereoselective-radical-perfluoroalkyltriflation-of-alkynes-using-phenyl-perfluoroalkyl-iodonium-triflates
#6
Xi Wang, Armido Studer
A method for regio- and stereoselective anti-addition of the perfluoroalkyl and the triflate group of phenyl(perfluoroalkyl)iodonium triflates to alkynes is presented. The radical reaction uses cheap CuCl as a smart initiator and can be conducted in gram scale. The perfluoroalkyltriflated products are readily further functionalized, rendering this transformation valuable.
May 18, 2017: Organic Letters
https://www.readbyqxmd.com/read/28516206/identification-expression-and-characterization-of-an-r-%C3%AF-transaminase-from-capronia-semiimmersa
#7
César Iglesias, Paola Panizza, Sonia Rodriguez Giordano
Chiral amines are essential precursors in the production of biologically active compounds, including several important drugs. Among the biocatalytic strategies that have been developed for their synthesis, the use of ω-transaminases (ω-TA) appears as an attractive alternative allowing the stereoselective amination of prochiral ketones. However, the problems associated with narrow substrate specificity, unfavourable reaction equilibrium and expensive amine donors still hamper its industrial application. The search for novel enzymes from nature can contribute to expand the catalytic repertoire of ω-TA and help to circumvent some of these problems...
May 17, 2017: Applied Microbiology and Biotechnology
https://www.readbyqxmd.com/read/28514163/palladium-catalyzed-%C3%AE-stereoselective-o-glycosylation-of-o-3-acylated-glycals
#8
Abhijit Sau, M Carmen Galan
Pd(MeCN)2Cl2 enables the α-stereoselective catalytic synthesis of 2,3-unsaturated O-glycosides from O(3)-acylated glycals without the requirement for additives to preactivate either donor or nucleophile. Mechanistic studies suggest that, unlike traditional (η3-allyl)palladium-mediated processes, the reaction proceeds via an alkoxy-palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is exemplified with the synthesis of a range of glycosides and glycoconjugates of synthetic utility...
May 17, 2017: Organic Letters
https://www.readbyqxmd.com/read/28513163/br%C3%A3-nsted-base-mediated-stereoselective-diphosphination-of-terminal-alkynes-with-diphosphanes
#9
Yuto Okugawa, Koji Hirano, Masahiro Miura
A Brønsted base mediated stereoselective diphosphination of terminal alkynes with diphosphanes proceeds to deliver the corresponding (E)-1,2-diphosphinoethenes in good yields. The reaction of aromatic alkynes occurs efficiently in the presence of a catalytic amount of LiO-t-Bu while MN(TMS)2 (M = Li or Na) gave better results in the case of aliphatic substrates. The Brønsted base mediated protocol can offer a good alternative to precedented transition-metal-catalyzed or radical-promoted approaches to the 1,2-diphosphinoethene framework of potent interest in catalysis and coordination chemistry...
May 17, 2017: Organic Letters
https://www.readbyqxmd.com/read/28513142/12-13-aziridinyl-epothilones-stereoselective-synthesis-of-trisubstituted-olefinic-bonds-from-methyl-ketones-and-heteroaromatic-phosphonates-and-design-synthesis-and-biological-evaluation-of-potent-antitumor-agents
#10
K C Nicolaou, Derek Rhoades, Yanping Wang, Ruoli Bai, Ernest Hamel, Monette Aujay, Joseph Sandoval, Julia Gavrilyuk
The synthesis and biological evaluation of a series of 12,13-aziridinyl epothilone B analogues is described. These compounds were accessed by a practical, general process that involved a 12,13-olefinic methyl ketone as a starting material obtained by ozonolytic cleavage of epothilone B followed by tungsten-induced deoxygenation of the epoxide moiety. The attachment of the aziridine structural motif was achieved by application of the Ess-Kürti-Falck aziridination, while the heterocyclic side chains were introduced via stereoselective phosphonate-based olefinations...
May 17, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28511039/occurrence-composition-source-and-regional-distribution-of-halogenated-flame-retardants-and-polybrominated-dibenzo-p-dioxin-dibenzofuran-in-the-soils-of-guiyu-china
#11
Pengjun Xu, Bu Tao, Zhiguang Zhou, Shuang Fan, Ting Zhang, Aimin Liu, Shuping Dong, Jingli Yuan, Hong Li, Jiping Chen, Yeru Huang
Guiyu, China, is well-known for the crude disposal of electronic waste (EW) and severe persistent organic pollutants (POPs). Therefore, in this study, the occurrence, composition, and source of polybrominated diphenyl ethers (PBDEs), 2,2',4,4',5,5'-hexabromobiphenyl (BB153), some novel brominated flame retardants (NBFRs), Dechlorane Plus (DP) and polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) in farmland soils covering Guiyu were studied. In EW disposal area soils, PBDEs were the most abundant FRs, with concentrations of 13-1014 ng g(-1)...
May 13, 2017: Environmental Pollution
https://www.readbyqxmd.com/read/28508443/stereoselective-synthesis-of-tetrasubstituted-alkenes-via-a-cp-co-iii-catalyzed-c-h-alkenylation-directing-group-migration-sequence
#12
Hideya Ikemoto, Ryo Tanaka, Ken Sakata, Motomu Kanai, Tatsuhiko Yoshino, Shigeki Matsunaga
A highly atom economical and stereoselective synthesis of tetrasubstituted α,β-unsaturated amides was achieved by a Cp*Co(III) -catalyzed C-H alkenylation/directing group migration sequence. A carbamoyl directing group, which is typically removed after C-H functionalization, worked as an internal acylating agent and migrated onto the alkene moiety of the product. The directing group migration was realized with the Cp*Co(III) catalyst, while a related Cp*Rh(III) catalyst did not promote the migration process...
May 16, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28507709/first-total-synthesis-of-concavine
#13
François Saint-Dizier, Nigel S Simpkins
The synthesis of the unusual alkaloid concavine, isolated from Clitocybe concava (Basidiomycetae), has been accomplished. The synthetic route features regio- and stereoselective manipulation of polycyclic imide intermediates via enolate substitution and Grignard addition, along with a key bridge-forming step involving a new method for sulfenylative radical cyclisation. The NMR data for synthetic concavine demonstrate that the original data reported for the natural product refer to the derived acetic acid salt, probably formed as an artefact of isolation or purification...
May 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28503355/stereoselective-cis-vinylcyclopropanation-via-a-gold-i-catalyzed-retro-buchner-reaction-under-mild-conditions
#14
Bart Herlé, Philipp M Holstein, Antonio M Echavarren
A highly stereoselective gold(I)-catalyzed cis-vinylcyclopropanation of alkenes has been developed. Allylic gold carbenes, generated via a retro-Buchner reaction of 7-alkenyl-1,3,5-cycloheptatrienes, react with alkenes to form vinylcyclopropanes. The gold(I)-catalyzed retro-Buchner reaction of these substrates proceeds by simple heating at a temperature much lower than that required for the reaction of 7-aryl-1,3,5-cycloheptatrienes (75 °C vs 120 °C). A newly developed Julia-Kocienski reagent enables the synthesis of the required cycloheptatriene derivatives in one step from readily available aldehydes or ketones...
May 5, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28498665/iron-phosphate-catalyzed-asymmetric-cross-dehydrogenative-coupling-of-2-naphthols-with-%C3%AE-ketoesters
#15
Sachin Narute, Doron Pappo
Chiral iron phosphate complexes were successfully exploited for asymmetric cross-dehydrogenative coupling reactions between 2-naphthols and β-ketoester derivatives. On the basis of kinetic studies, it is suggested that iron monophosphate complexes constitute the active catalysts that induce stereoselectivity during the carbon-carbon bond-formation step.
May 12, 2017: Organic Letters
https://www.readbyqxmd.com/read/28497972/organocatalytic-asymmetric-annulation-between-hydroxymaleimides-and-nitrosoarenes-stereoselective-preparation-of-chiral-quaternary-n-hydroxyindolines
#16
Yu Yang, Hong-Xia Ren, Feng Chen, Zheng-Bing Zhang, Ying Zou, Chao Chen, Xiang-Jia Song, Fang Tian, Lin Peng, Li-Xin Wang
An unusual and highly effective asymmetric annulation of nitrosoarenes with hydroxymaleimides catalyzed by a chiral bifunctional amine squaramide catalyst has been disclosed. A wide range of highly fused chiral N-hydroxyindolines with two consecutive quaternary stereocenters and multifunctional groups were directly and effectively prepared in excellent yields (up to >99%) with complete regioselective cyclization and excellent stereoselectivities (up to >99:1 dr and >99% ee). The efficiency and potentials of the new reaction and the target chiral entities were well demonstrated by delicate transformations into a series of new chiral indolines...
May 12, 2017: Organic Letters
https://www.readbyqxmd.com/read/28493619/access-to-hexahydrocarbazoles-the-thorpe-ingold-effects-of-the-ligand-on-enantioselectivity
#17
Hao Chen, Lijia Wang, Feng Wang, Liu-Peng Zhao, Pan Wang, Yong Tang
A novel cyclization reaction of methylenemalonate with indoles is reported, and it provides efficient access to a variety of hexahydrocarbazoles. The enantioselective version was realized by a finely tuned ligand/Cu(II) catalyst. The optically active hexahydrocarbazoles contain three quaternary carbon centers and are obtained in up to 99 % yield with greater than 99:1 d.r. and up to greater than 99 % ee. This reaction can be carried out on gram scale and stereoselective transformation of the product led to the core structure of a series of alkaloids from Kopsia plants...
May 11, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28492314/the-synthesis-of-chiral-%C3%AE-%C3%AE-diaryl-allylic-alcohols-and-their-use-in-the-preparation-of-%C3%AE-tertiary-allylamines-and-quaternary-%C3%AE-amino-acids
#18
Michał Pieczykolan, Aleksandra Narczyk, Sebastian Stecko
An approach to non-racemic β,β-diarylsubstituted allyl alcohols is described. Their synthesis starts from L-lactic acid-derived propargyl alcohol which is submitted to sequential Sonogashira/Suzuki or Sonagashira/Stille coupling reactions. Both approaches enable the synthesis either (Z)- or (E)-allylic alcohols regarding and order of an introducing coupling agents. The obtained allyl alcohols were applied in synthesis of non-racemic α-tertiary allylamines via stereocontrolled cyanate-to-isocyanate sigmatropic rearrangement reaction of the corresponding allyl carbamates...
May 11, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28488866/mechanism-regio-and-diastereoselectivity-of-rh-iii-catalyzed-cyclization-reactions-of-n-arylnitrones-with-alkynes-a-dft-study
#19
Yingzi Li, Chunhui Shan, Yun-Fang Yang, Fu-Qiang Shi, Xiaotian Qi, Kendall N Houk, Yu Lan
Nitrones have been used for rhodium-catalyzed cyclization C-H bond activation and O-atom transfer of arylnitrones with alkynes by Chang et al. Density functional theory (DFT) method has been used to study the mechanism, regio-, and diastereoselectivity of type reactions. The results elucidated that the reaction pathway for Rh(III)-catalyzed cyclization of N-arylnitrones with alkyne contains a C-H bond activation, an alkyne insertion into Rh-C bond, a reductive elimination to form an Rh(I) complex, an oxidative addition leading to N-O cleavage, an imine insertion into the Rh-C bond and the final protonolysis to regenerate the products and the active catalyst...
May 10, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28487071/diversity-oriented-sustainable-synthesis-of-antimicrobial-spiropyrrolidine-thiapyrrolizidine-oxindole-derivatives-new-ligands-for-a-metallo-%C3%AE-lactamase-from-klebsiella-pneumonia
#20
Anshu Dandia, Shahnawaz Khan, Pragya Soni, Aayushi Indora, Dinesh Kumar Mahawar, Prateek Pandya, Chetan Singh Chauhan
A simple, environmentally benign and highly proficient microwave assisted one-pot approach for the synthesis of antimicrobial spiropyrrolidine/thiapyrrolizidine oxindole derivatives is reported assembling two pharmacophoric moieties (1,3-indanedione and pyrrolidine/thiapyrrolizidine) in a single molecular framework via three-component 1,3-dipolar cycloaddition reaction of substituted isatin, sarcosine/1,3-thiazoles-4-carboxylic acid and Knoevenagel adduct (2-Cyano-3-phenyl-acrylic acid ethyl ester or 2-Benzylidene-malononitrile) in 2,2,2-trifluoroethanol as a reusable green solvent...
April 27, 2017: Bioorganic & Medicinal Chemistry Letters
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