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Advanced Synthesis & Catalysis

György Keglevich, Réka Henyecz, Zoltán Mucsi, Nóra Zs Kiss
It was proved by our experiments that on microwave irradiation, the mono- or bidentate phosphorus ligands generally applied in the palladium(II)-catalyzed P-C coupling reaction of aryl bromides and dialkyl phosphites or secondary phosphine oxides may be substituted by the excess of the >P(O)H reagent that exists under a tautomeric equilibrium. Taking into account that the reduction of the palladium(II) salt and the ligation of the palladium(0) so formed requires 3 equivalents of the P-species for the catalyst applied in a quantity of 5-10%, all together, 15-30% of the P-reagent is necessary beyond its stoichiometric quantity...
December 19, 2017: Advanced Synthesis & Catalysis
Zsófia Bata, Renzhe Qian, Alexander Roller, Jeannie Horak, László Csaba Bencze, Csaba Paizs, Friedrich Hammerschmidt, Beáta G Vértessy, László Poppe
Aromatic amino acid ammonia-lyases and aromatic amino acid 2,3-aminomutases contain the post-translationally formed prosthetic 3,5-dihydro-4-methylidene-5H-imidazol-5-one (MIO) group. MIO enzymes catalyze the stereoselective synthesis of α- or β-amino acid enantiomers, making these chemical processes environmentally friendly and affordable. Characterization of novel inhibitors enables structural understanding of enzyme mechanism and recognizes promising herbicide candidates as well. The present study found that both enantiomers of the aminophosphonic acid analogue of the natural substrate phenylalanine and a novel derivative bearing a methylidene at the β-position inhibited phenylalanine ammonia-lyases (PAL), representing MIO enzymes...
June 19, 2017: 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
Keyume Ablajan, Grace B Panetti, Xiaodong Yang, Byeong-Seon Kim, Patrick J Walsh
The direct arylation of weakly acidic sp3-hybridized C-H bonds via deprotonated cross-coupling processes (DCCP) is a challenge. Herein, a Pd(NIXANTPHOS)-based catalyst for the mono arylation of 4-pyridylmethyl 2-aryl ethers to generate diarylated 4-pyridyl methyl ethers is introduced. Furthermore, under similar conditions, the diarylation of 4-pyridylmethyl ethers with aryl bromides has been developed. These methods enable the synthesis of new pyridine derivatives, which are common in medicinally active compounds and in application in materials science...
June 6, 2017: Advanced Synthesis & Catalysis
Rick C Betori, Eric R Miller, Karl A Scheidt
A novel biocatalytic system to access a wide variety of β-hydroxydioxinones from β-ketodioxinones employing commercial engineered ketoreductases has been developed. This practical system provides a remarkably straightforward solution to limitations in accessing certain chemical scaffolds common in β-hydroxydioxinones that are of great interest due to their diversification capabilities. A few highlights of this system are that it is high yielding, highly enantioselective, and chromatography-free. We have demonstrated both a wide substrate scope and a high degree of scalability...
April 3, 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
Matthew N Pennell, Michael P Kyle, Samantha M Gibson, Louise Male, Peter G Turner, Richard S Grainger, Tom D Sheppard
The regioselective gold-catalysed hydration of propargylic alcohols to β-hydroxy ketones can be achieved by diverting the gold-catalysed Meyer-Schuster rearrangement through the addition of a protic additive with a pKa of 7-9 such as p-nitrophenol, boric acid or a boronic acid. This provides an interesting alternative to an aldol reaction when combined with the straightforward addition of an alkyne to an aldehyde or ketone. The gold-catalysed reaction of an electron-deficient, sterically hindered propargylic alcohol with a boronic acid led to the formation of an unusually stable cyclic boron enolate...
April 28, 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
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