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Advanced Synthesis & Catalysis

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https://www.readbyqxmd.com/read/27594819/a-ruthenium-catalyst-for-olefin-metathesis-featuring-an-anti-bredt-n-heterocyclic-carbene-ligand
#1
David Martin, Vanessa M Marx, Robert H Grubbs, Guy Bertrand
A ruthenium complex bearing an "anti-Bredt" N-heterocyclic carbene was synthesized, characterized and evaluated as a catalyst for olefin metathesis. Good conversions were observed at room temperature for the formation of di- and tri-substituted olefins by ring-closing metathesis. It also allowed for the ring-opening metathesis polymerization of cyclooctadiene, as well as for the cross-metathesis of cis-1,4-diacetoxy-2-butene with allyl-benzene, with enhanced Z/E kinetic selectivity over classical NHC-based catalysts...
March 17, 2016: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/27325912/simplified-preparation-of-trialkylvinylsilanes-via-the-silyl-heck-reaction-utilizing-a-second-generation-catalyst
#2
Jesse R McAtee, Sarah B Krause, Donald A Watson
Recently we reported a second-generation ligand, bis(3,5-di-tert-butylphenyl)(tert-butyl)phosphine, for the preparation of allyl silanes using the silyl-Heck reaction. We now show that this new ligand also provides superior reactivity in the preparation of vinylsilanes from styrene derivatives. For the first time, this new ligand provides exceptionally high yields of trialkylvinylsilanes using a widely available palladium pre-catalyst, Pd2(dba)3. Finally, we demonstrate that this new catalyst system is able to form more highly decorated all carbon substituted vinylsilanes that have been shown to possess superior reactivity in oxidation and cross coupling reactions...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/27134619/rhodium-i-catalyzed-intermolecular-hydroacylation-of-%C3%AE-keto-amides-and-isatins-with-non-chelating-aldehydes
#3
Kevin G M Kou, Lauren E Longobardi, Vy M Dong
The application of the bidentate, electron-rich bisphosphine ligand, 1,3-bis(dicyclohexyl)phosphine-propane (dcpp), in rhodium(I)-catalyzed intermolecular ketone hydroacylation is herein described. Isatins and α-keto amides are shown to undergo hydroacylation with a variety of non-chelating linear and branched aliphatic aldehydes. Also reported is the synthesis of new bidentate chiral phosphine ligands, and their application in hydroacylation is discussed.
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/27042171/an-efficient-protocol-for-the-palladium-catalyzed-asymmetric-decarboxylative-allylic-alkylation-using-low-palladium-concentrations-and-a-palladium-ii-precatalyst
#4
Alexander N Marziale, Douglas C Duquette, Robert A Craig, Kelly E Kim, Marc Liniger, Yoshitaka Numajiri, Brian M Stoltz
Enantioselective catalytic allylic alkylation for the synthesis of 2-alkyl-2-allylcycloalkanones and 3,3-disubstituted pyrrolidinones, piperidinones and piperazinones has been previously reported by our laboratory. The efficient construction of chiral all-carbon quaternary centers by allylic alkylation was previously achieved with a catalyst derived in situ from zero valent palladium sources and chiral phosphinooxazoline (PHOX) ligands. We now report an improved reaction protocol with broad applicability among different substrate classes in industry-compatible reaction media using loadings of palladium(II) acetate as low as 0...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26622222/palladium-catalyzed-alkene-carboamination-reactions-of-electron-poor-nitrogen-nucleophiles
#5
Luke J Peterson, John P Wolfe
Modified reaction conditions that facilitate Pd-catalyzed alkene carboamination reactions of electron-deficient nitrogen nucleophiles are reported. Pent-4-enylamine derivatives bearing N-tosyl or N-trifluoroacetyl groups are coupled with aryl triflates to afford substituted pyrrolidines in good yield. These reactions proceed via a mechanism involving anti-aminopalladation of the alkene, which differs from previously reported analogous reactions of N-aryl and N-boc pentenylamines. The application of these conditions to a formal synthesis of (±)-aphanorphine is also described...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26622221/diastereoselective-oxidative-c-n-c-o-and-c-n-c-n-bond-formation-tandems-initiated-by-visible-light-synthesis-of-fused-n-arylindolines
#6
Scott A Morris, Theresa H Nguyen, Nan Zheng
The synthesis of fused N-arylindolines using visible light photoredox catalysis has been developed. We previously described that photogenerated amine radical cations generate substituted indoles through an intermediate benzylic carbocation. Herein, we expand the application of this chemistry by trapping the benzylic carbocation with tethered heteronucleophiles. The reactivity of the photogenerated benzylic carbocation is explored and applied to a range of substrates with various electronic characters and ring constraints...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26543444/a-synergistic-combinatorial-and-chiroptical-study-of-peptide-catalysts-for-asymmetric-baeyer-villiger-oxidation
#7
Michael W Giuliano, Chung-Yon Lin, David K Romney, Scott J Miller, Eric V Anslyn
We report an approach to the asymmetric Baeyer-Villiger oxidation utilizing bioinformatics-inspired combinatorial screening for catalyst discovery. Scaled-up validation of our on-bead efforts with a circular dichroism-based assay of alcohols derived from the products of solution-phase reactions established the absolute configuration of lactone products; this assay proved equivalent to HPLC in its ability to evaluate catalyst performance, but was far superior in its speed of analysis. Further solution-phase screening of a focused library suggested a mode of asymmetric induction that draws distinct parallels with the mechanism of Baeyer-Villiger monooxygenases...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26347405/palladium-catalyzed-synthesis-of-2-3-disubstituted-benzofurans-an-approach-towards-the-synthesis-of-deuterium-labeled-compounds
#8
Soumitra Agasti, Soham Maity, Kalman J Szabo, Debabrata Maiti
Palladium-catalyzed oxidative annulations between phenols and alkenylcarboxylic acids produced a library of benzofuran compounds. Depending on the nature of the substitution of the phenol precursor, either 2,3-dialkylbenzofurans or 2-alkyl-3-methylene-2,3-dihydrobenzofurans can be synthesized with excellent regioselectivity. Reactions between conjugated 5-phenylpenta-2,4-dienoic acids and phenol gave 3-alkylidenedihydrobenzofuran alkaloid motifs while biologically active 7-arylbenzofuran derivatives were prepared by starting from 2-phenylphenols...
July 6, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26622223/exploiting-enzymatic-dynamic-reductive-kinetic-resolution-dyrkr-in-stereocontrolled-synthesis
#9
Gregory A Applegate, David B Berkowitz
Over the past two decades, the domains of both frontline synthetic organic chemistry and process chemistry and have seen an increase in crosstalk between asymmetric organic/organometallic approaches and enzymatic approaches to stereocontrolled synthesis. This review highlights the particularly auspicious role for dehydrogenase enzymes in this endeavor, with a focus on dynamic reductive kinetic resolutions (DYRKR) to "deracemize" building blocks, often setting two stereocenters in so doing. The scope and limitations of such dehydrogenase-mediated processes are overviewed, as are future possibilities for the evolution of enzymatic DYRKR...
May 26, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26190963/regioselective-enzymatic-%C3%AE-carboxylation-of-para-hydroxy-styrene-derivatives-catalyzed-by-phenolic-acid-decarboxylases
#10
Christiane Wuensch, Tea Pavkov-Keller, Georg Steinkellner, Johannes Gross, Michael Fuchs, Altijana Hromic, Andrzej Lyskowski, Kerstin Fauland, Karl Gruber, Silvia M Glueck, Kurt Faber
We report on a 'green' method for the utilization of carbon dioxide as C1 unit for the regioselective synthesis of (E)-cinnamic acids via regioselective enzymatic carboxylation of para-hydroxystyrenes. Phenolic acid decarboxylases from bacterial sources catalyzed the β-carboxylation of para-hydroxystyrene derivatives with excellent regio- and (E/Z)-stereoselectivity by exclusively acting at the β-carbon atom of the C=C side chain to furnish the corresponding (E)-cinnamic acid derivatives in up to 40% conversion at the expense of bicarbonate as carbon dioxide source...
May 26, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25729343/mild-and-general-access-to-diverse-1h-benzotriazoles-via-diboron-mediated-n-oh-deoxygenation-and-palladium-catalyzed-c-c-and-c-n-bond-formation
#11
Venkateshwarlu Gurram, Hari K Akula, Ramesh Garlapati, Narender Pottabathini, Mahesh K Lakshman
Benzotriazoles are a highly important class of compounds with broad-ranging applications in such diverse areas as medicinal chemistry, as auxiliaries in organic synthesis, in metallurgical applications, in aircraft deicing and brake fluids, and as antifog agents in photography. Although there are numerous approaches to N-substituted benzotriazoles, the essentially one general method to N-unsubstituted benzotriazoles is via diazotization of o-phenylenediamines, which can be limited by the availability of suitable precursors...
February 9, 2015: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26190959/enzymatic-redox-cascade-for-one-pot-synthesis-of-uridine-5-diphosphate-xylose-from-uridine-5-diphosphate-glucose
#12
Thomas Eixelsberger, Bernd Nidetzky
Synthetic ways towards uridine 5'-diphosphate (UDP)-xylose are scarce and not well established, although this compound plays an important role in the glycobiology of various organisms and cell types. We show here how UDP-glucose 6-dehydrogenase (hUGDH) and UDP-xylose synthase 1 (hUXS) from Homo sapiens can be used for the efficient production of pure UDP-α-xylose from UDP-glucose. In a mimic of the natural biosynthetic route, UDP-glucose is converted to UDP-glucuronic acid by hUGDH, followed by subsequent formation of UDP-xylose by hUXS...
November 24, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26185491/reversed-polarity-synthesis-of-diaryl-ketones-through-palladium-catalyzed-direct-arylation-of-2-aryl-1-3-dithianes
#13
Baris Yucel, Patrick J Walsh
An umpolung approach to the synthesis of diaryl ketones has been developed based on in situ generation of acyl anion equivalents and their catalytic arylation. This method entails the base promoted palladium catalyzed direct C-H arylation of 2 The resulting 2,2-diaryl-1,3-dithianes with aryl bromides. Use of MN(SiMe3)2 (M=Li, Na) base results in reversible deprotonation of the weakly acidic dithiane. In the presence of a Pd(NiXantphos)-based catalyst and aryl bromide, cross-coupling of the metallated 2-aryl-1,3-dithiane takes place under mild conditions (2 h at rt) with yields as high as 96%...
November 24, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/26120292/intermolecular-3-2-annulation-of-cyclopropylanilines-with-alkynes-enynes-and-diynes-via-visible-light-photocatalysis
#14
Theresa H Nguyen, Scott A Morris, Nan Zheng
One-step synthesis of carbocycles substituted with amines from simple starting materials remains rare. We recently developed intermolecular [3+2] annulation of cyclopropylanilines with alkenes and alkynes that enable this one-step synthesis. Herein, we report our findings for a fullscale study of the annulation. Significant expansion of the substrate scope for both cyclopropylanilines and alkynes is achieved. A range of structurally diverse carbocycles substituted with amines is prepared.
September 15, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25685127/palladium-catalyzed-direct-%C3%AE-aryation-of-benzyl-thioethers-with-aryl-bromides
#15
Gustavo Frensch, Nusrah Hussain, Francisco A Marques, Patrick J Walsh
The arylation of sp(3)-hybridized C-H's bonds is a powerful strategy to build molecular complexity and diversity. A novel and efficient palladium-catalyzed direct sp(3) C-H arylation of aryl and alkyl benzyl thioether derivatives with aryl bromides is reported. The reaction involves reversible deprotonation of the benzylic C-H's of the thioether with either LiN(SiMe3)2 or NaN(SiMe3)2 and subsequent cross-coupling to provide the functionalized products in up to 97% yield. A screen of 24 of the most successful ligands in cross-coupling chemistry led to the identification of NiXantPhos as the only viable ligand for this challenging coupling...
August 11, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25484848/6-azabicyclo-3-2-1-octanes-via-copper-catalyzed-enantioselective-alkene-carboamination
#16
Barbara J Casavant, Azade S Hosseini, Sherry R Chemler
Bridged bicyclic rings containing nitrogen heterocycles are important motifs in bioactive small organic molecules. An enantioselective copper-catalyzed alkene carboamination reaction that creates bridged heterocycles is reported herein. Two new rings are formed in this alkene carboamination reaction where N-sulfonyl-2-aryl-4-pentenamines are converted to 6-azabicyclo[3.2.1]octanes using [Ph-Box-Cu](OTf)2 or related catalysts in the presence of MnO2 as stoichiometric oxidant in moderate to good yields and generally excellent enantioselectivities...
August 11, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25414624/transition-metal-free-ipso-functionalization-of-arylboronic-acids-and-derivatives
#17
Chen Zhu, John R Falck
Arylboronic acids and their derivatives have been widely exploited as important synthetic precursors in organic synthesis, materials science, and pharmaceutical development. In addition to numerous applications in transition-metal-mediated cross-coupling reactions, transition-metal-free transformations involving arylboronic acids and derivatives have recently received a surge of attention for converting the C-B bond to C-C, C-N, C-O, and many other C-X bonds. Consequently, a wide range of useful compounds, e...
August 11, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25505857/metal-free-preparation-of-cycloalkyl-aryl-sulfides-via-di-tert-butyl-peroxide-promoted-oxidative-c-sp3-bond-h-bond-thiolation-of-cycloalkanes
#18
Jincan Zhao, Hong Fang, Jianlin Han, Yi Pan, Guigen Li
A concise thiolation of C(sp(3))-H bond of cycloalkanes with diaryl disulfides in the presence of oxidant of di-tert-butylperoxide (DTBP) has been developed. This reaction without using any of metal catalyst, tolerates varieties of disulfides and cycloalkanes substrates, giving good to excellent chemical yields, which provides a useful approach to cycloalkyl aryl sulfides from unactivated cycloalkanes.
August 10, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25484847/catalytic-isonitrile-insertions-and-condensations-initiated-by-rnc-x-complexation
#19
Suravi Chakrabarty, Shruti Choudhary, Arpit Doshi, Fa-Qiang Liu, Rishabh Mohan, Manasa P Ravindra, Dhruv Shah, Xun Yang, Fraser F Fleming
Isonitriles are delicately poised chemical entities capable of being coaxed to react as nucleophiles or electrophiles. Directing this tunable reactivity with metal and non-metal catalysts provides rapid access to a large array of complex nitrogenous structures ideally functionalized for medicinal applications. Isonitrile insertion into transition metal complexes has featured in numerous synthetic and mechanistic studies, leading to rapid deployment of isonitriles in numerous catalytic processes, including multicomponent reactions (MCR)...
July 7, 2014: Advanced Synthesis & Catalysis
https://www.readbyqxmd.com/read/25419207/regioselective-benzylation-of-2-deoxy-2-aminosugars-using-crown-ethers-application-to-a-shortened-synthesis-of-hyaluronic-acid-oligomers
#20
Chinmoy Mukherjee, Lin Liu, Nicola L B Pohl
The combination of benzyl bromide, sodium hydroxide and 15-crown-5 in tetrahydrofuran is shown to be an efficient method for installing benzyl groups at both the 4- and 6-positions regioselectively directly from peracetylated N-trichloroacetyl-protected glucosamine and galactosamine. Application of this benzylation strategy proved to significantly shorten the synthetic route to hyaluronic acid tetra- and hexamers.
July 7, 2014: Advanced Synthesis & Catalysis
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