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Advanced Synthesis & Catalysis

Stefan E Payer, Xiang Sheng, Hannah Pollak, Christiane Wuensch, Georg Steinkellner, Fahmi Himo, Silvia M Glueck, Kurt Faber
The catalytic promiscuity of a ferulic acid decarboxylase from Enterobacter sp. (FDC_Es) and phenolic acid decarboxylases (PADs) for the asymmetric conjugate addition of water across the C=C bond of hydroxystyrenes was extended to the N-, C- and S-nucleophiles methoxyamine, cyanide and propanethiol to furnish the corresponding addition products in up to 91% ee. The products obtained from the biotransformation employing the most suitable enzyme/nucleophile pairs were isolated and characterized after optimizing the reaction conditions...
June 19, 2017: Advanced Synthesis & Catalysis
Katharina Plasch, Verena Resch, Julien Hitce, Jarosław Popłoński, Kurt Faber, Silvia M Glueck
In order to extend the applicability of the regioselective enzymatic carboxylation of phenols, the substrate scope of o-benzoic acid (de)carboxylases has been investigated towards complex molecules with an emphasis on flavouring agents and polyphenols possessing antioxidant properties. o-Hydroxycarboxylic acid products were obtained with perfect regioselectivity, in moderate to excellent yields. The applicability of this method was proven by the regioselective bio-carboxylation of resveratrol on a preparative scale with 95% yield...
March 20, 2017: Advanced Synthesis & Catalysis
Duc Duy Vo, Mikael Elofsson
Resveratrol-based natural products constitute a valuable source of unique compounds with diverse biological activities. In this report we investigate demethylation strategies to minimize formation of cyclized and dimerized products during the synthesis of viniferifuran and analogues. We found that boron trichloride/tetra-n-butylammonium iodide (BCl3/TBAI) is typically more effective than boron tribromide (BBr3). Based on these findings we carried out the first syntheses of dehydro-δ-viniferin, resveratrol-piceatannol hybrid and anigopreissin A...
December 22, 2016: Advanced Synthesis & Catalysis
Melvyn B Ansell, George E Kostakis, Holger Braunschweig, Oscar Navarro, John Spencer
The bis(N-heterocyclic carbene)(diphenylacetylene)palladium complex [Pd(ITMe)2(PhC≡CPh)] (ITMe=1,3,4,5-tetramethylimidazol-2-ylidene) acts as a highly active pre-catalyst in the diboration and silaboration of azobenzenes to synthesize a series of novel functionalized hydrazines. The reactions proceed using commercially available diboranes and silaboranes under mild reaction conditions.
December 7, 2016: Advanced Synthesis & Catalysis
Daniel Schwendenwein, Giuseppe Fiume, Hansjörg Weber, Florian Rudroff, Margit Winkler
The enzymatic reduction of carboxylic acids is in its infancy with only a handful of biocatalysts available to this end. We have increased the spectrum of carboxylate-reducing enzymes (CARs) with the sequence of a fungal CAR from Neurospora crassa OR74A (NcCAR). NcCAR was efficiently expressed in E. coli using an autoinduction protocol at low temperature. It was purified and characterized in vitro, revealing a broad substrate acceptance, a pH optimum at pH 5.5-6.0, a Tm of 45 °C and inhibition by the co-product pyrophosphate which can be alleviated by the addition of pyrophosphatase...
November 3, 2016: Advanced Synthesis & Catalysis
Jacqueline Jiménez, Byeong-Seon Kim, Patrick J Walsh
Isoindolinones comprise an important class of medicinally active compounds. Herein we report a straightforward functionalization of the isoindolinones with aryl bromides (22 examples) using a Pd(OAc)2/NIXANTPHOS-based catalyst system. Additionally 3-aryl 3-hydroxy isoindolinone derivatives, which exhibit anti-tumor activity, can be accessed via a tandem reaction. Thus, when the arylation product is exposed to air under basic conditions, in situ oxidation takes place to install the 3-hydroxyl group. Furthermore, a tandem arylation/allylic substitution reaction is advanced in which both the arylation and allylic substitution are catalyzed by the same palladium catalyst...
September 1, 2016: Advanced Synthesis & Catalysis
Wen-Bo Chen, Chun-Hui Xing, Jie Dong, Qiao-Sheng Hu
The use of electron-poor, fluoro-containing arylboronic acids as general coupling partners for nickel(0) /tricyclohexylphosphine-catalyzed cross-coupling of aryl arenesulfonates is described. Electron-poor fluoro-containing arylboronic acids were found to react, faster than electron-rich/neutral arylboronic acids, with (4-methoxyphenyl)(4-methylbenzenesulfonato-κO)bis(tricyclohexylphosphine)nickel. Bis(1,5-cyclooctadiene)nickel(0)/tricyclohexylphosphine, (4-methoxyphenyl)(4-methylbenzenesulfonato-κO)bis(tricyclohexylpho sphine)nickel and bis(tricyclohexylphosphine)nickel (II) bromide were all found to be efficient catalysts/catalyst precursors...
June 30, 2016: Advanced Synthesis & Catalysis
Bing Zheng, Minyan Li, Gui Gao, Yuying He, Patrick J Walsh
A Palladium-catalyzed α-arylation of sulfonamides with aryl chlorides is presented. A Buchwald type precatalyst formed with Kwong's indole-based ligand enabled this transformation to be compatible with a large variety of methyl sulfonamides and aryl chlorides in good to excellent yields. Importantly, under the optimized reaction conditions, only mono-arylated products were observed. This method has been applied to the efficient synthesis of sumatriptan, which is used to treat migraines.
June 30, 2016: Advanced Synthesis & Catalysis
Minyan Li, Baris Yucel, Jacqueline Jiménez, Madeline Rotella, Yue Fu, Patrick J Walsh
An umpolung synthesis of diarylmethylamine derivatives is presented. This reaction entails a Pd catalyzed arylation of 1,3-diaryl-2-azaallyl anions, in situ generated from N-benzyl aldimines. A Pd(NIXANTPHOS)-based catalyst together with hindered silylamide bases enabled the coupling of aldimines with aryl bromides in good to excellent yields without product isomerization. Moreover, regioselectivity in the arylation of unsymmetrical 1,3-diaryl-2-azaallyl anions was studied. This method is suitable for a gram scale synthesis of diarylmethylamine derivatives at room temperature without use of a glovebox...
June 16, 2016: Advanced Synthesis & Catalysis
Patrick M Barbour, Wei Wang, Le Chang, Kasey L Pickard, Rana Rais, Barbara S Slusher, Xiang Wang
Antibiotic resistance is a worldwide public health threat that needs to be addressed by improved antibiotic stewardship and continuing development of new chemical entities to treat resistant bacterial infections. Compounds that work alongside known antibiotics as combination therapies offer an efficient and sustainable approach to counteract antibiotic resistance in bacteria. Guided by property-based analysis, a series of aza-tricyclic indolines (ATIs) were synthesized to optimize their physiochemical properties as novel combination therapies with β-lactams to treat methicillin-resistant S...
April 28, 2016: Advanced Synthesis & Catalysis
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
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
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
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
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
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
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
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
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
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
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