journal
https://read.qxmd.com/read/33162875/asymmetric-nazarov-cyclizations-of-unactivated-dienones-by-hydrogen-bond-donor-lewis-acid-co-catalyzed-enantioselective-proton-transfer
#21
JOURNAL ARTICLE
Jan B Metternich, Martin Reiterer, Eric N Jacobsen
We report an enantioselective Nazarov cyclization catalyzed by chiral hydrogen-bond-donors in concert with silyl Lewis acids. The developed transformation provides access to tri-substituted cyclopentenones in high levels of enantioselectivity (up to 95% e.e.) from a variety of simple unactivated dienones. Kinetic and mechanistic studies are consistent with a reversible 4π-electrocyclization C-C bond-forming step followed by rate- and enantio-determining proton-transfer as the mode of catalysis.
October 6, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32982624/hydroalkylation-of-aryl-alkenes-with-organohalides-catalyzed-by-molybdenum-oxido-based-lewis-pairs
#22
JOURNAL ARTICLE
Niklas Zwettler, Antoine Dupé, Sumea Klokić, Angela Milinković, Dado Rodić, Simon Walg, Dmytro Neshchadin, Ferdinand Belaj, Nadia C Mösch-Zanetti
Three molybdenum(VI) dioxido complexes [MoO2 (L)2 ] bearing Schiff base ligands were reacted with B(C6 F5 )3 to afford the corresponding adducts [MoO{OB(C6 F5 )3 }(L)2 ], which were fully characterized. They exhibit Frustrated Lewis-Pairs reactivity when reacting with silanes. Especially, the [MoO{OB(C6 F5 )3 }(L)2 ] complex with L=2,4-dimethyl-6-((phenylimino)methyl)phenol proved to be active as catalyst for the hydroalkylation of aryl alkenes with organohalides and for the Atom-Transfer Radical Addition (ATRA) of organohalides to aliphatic alkenes...
August 4, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32612487/radical-induced-1-2-migrations-of-boron-ate-complexes
#23
REVIEW
Marvin Kischkewitz, Florian W Friese, Armido Studer
1,2-Boron ate rearrangements represent a fundamental class of transformations to establish new C-C bonds while retaining the valuable boron moiety in the product. In established ionic processes, the boron ate complex is activated by an external electrophile to induce a 1,2-migration from boron to an adjacent sp 3 or sp 2 carbon atom. Recently, two complementary radical polar crossover approaches have been explored for both classes, 1,2-migrations to sp 2 and sp 3 carbon centers. This review describes the general concepts in this emerging research field and summarizes recent developments of radical-induced 1,2-migrations from boron to carbon...
May 26, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32421034/continuous-flow-bioamination-of-ketones-in-organic-solvents-at-controlled-water-activity-using-immobilized-%C3%AF-transaminases
#24
JOURNAL ARTICLE
Wesley Böhmer, Alexey Volkov, Karim Engelmark Cassimjee, Francesco G Mutti
Compared with biocatalysis in aqueous media, the use of enzymes in neat organic solvents enables increased solubility of hydrophobic substrates and can lead to more favorable thermodynamic equilibria, avoidance of possible hydrolytic side reactions and easier product recovery. ω-Transaminases from Arthrobacter sp . (AsR-ωTA) and Chromobacterium violaceum (Cv-ωTA) were immobilized on controlled porosity glass metal-ion affinity beads (EziG) and applied in neat organic solvents for the amination of 1-phenoxypropan-2-one with 2-propylamine...
April 27, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32322184/technology-trends-of-catalysts-in-hydrogenation-reactions-a-patent-landscape-analysis
#25
REVIEW
Marius A Stoffels, Felix J R Klauck, Thomas Hamadi, Frank Glorius, Jens Leker
The purpose of this review is to present an overview of the patent landscape for catalysts used in hydrogenation reactions. Based on patent data extracted from PatBase®, we use predefined patent classifications as well as a keyword-based search for our analyses. The results indicate that the number of patent families that protect heterogeneous catalysts grows twice as fast as that for their homogeneous counterparts. Furthermore, the data show a shift towards abundant and non-toxic elements in heterogeneous catalysis, while the noble metals continue to dominate the patent landscape of homogeneous catalysis...
March 17, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/34093103/enantioselective-kinetic-resolution-desymmetrization-of-para-quinols-a-case-study-in-boronic-acid-directed-phosphoric-acid-catalysis
#26
JOURNAL ARTICLE
Banruo Huang, Ying He, Mark D Levin, Jaime A S Coelho, Robert G Bergman, F Dean Toste
A chiral phosphoric acid-catalyzed kinetic resolution and desymmetrization of para -quinols operating via oxa-Michael addition was developed and subsequently subjected to mechanistic study. Good to excellent s -factors/enantioselectivities were obtained over a broad range of substrates. Kinetic studies were performed, and DFT studies favor a hydrogen bonding activation mode. The mechanistic studies provide insights to previously reported chiral anion phase transfer reactions involving chiral phosphate catalysts in combination with boronic acids...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/33692657/palladium-catalyzed-enantioselective-decarboxylative-allylic-alkylation-of-protected-benzoin-derived-enol-carbonates
#27
JOURNAL ARTICLE
Rémi Lavernhe, Eric J Alexy, Haiming Zhang, Brian M Stoltz
The enantioselective palladium-catalyzed decarboxylative allylic alkylation of fully substituted α-hydroxy acyclic enol carbonates providing tetrasubstituted benzoin derivatives is reported. Investigation into the transformation revealed that preparation of the starting material as a single enolate isomer is crucial for optimal enantioselectivity. The obtained alkylation products contain multiple reactive sites that can be utilized toward the synthesis of stereochemically rich derivatives. COMMUNICATION.
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/33447174/enantioselective-synthesis-of-%C3%AE-functionalized-cyclopentenones-and-%C3%AE-functionalized-cycloheptenones-utilizing-a-redox-relay-heck-strategy
#28
JOURNAL ARTICLE
Qianjia Yuan, Matthew B Prater, Matthew S Sigman
In this report, the desymmetrization of cyclic enones under relay Heck conditions with an array of aryl boronic acids, alkenyl triflates and indole derivatives is described. This method grants facile access to diverse γ-functionalized cyclopentenones and δ-functionalized cycloheptenones. Using this approach, a formal synthesis of ( S )-baclofen was completed in high yield and excellent enantioselectivity.
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/33192219/cobalt-catalyzed-reductive-spirocyclopropanation-reactions
#29
JOURNAL ARTICLE
Jacob Werth, Kristen Berger, Christopher Uyeda
Cobalt pyridine-diimine (PDI) complexes catalyze the reductive spirocyclopropanation of terminal 1,3-dienes. gem -Dichlorocycloalkanes serve as carbene precursors and Zn is used as a terminal electron source. The reaction is effective for a range of gem -dichloro partners including those containing sulfur and nitrogen heterocycles. An example of an intramolecular Rh-catalyzed [5 + 2]-cycloaddition of a vinyl spirocyclopropane is demonstrated, providing rapid access to a complex tricyclic framework. Overall, this catalyst system is capable of suppressing the kinetically facile 1,2-hydride shift, which has hampered the development of Simmons-Smith reactions using Zn carbenoids possessing β-hydrogen atoms...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32431586/pyridine-diimine-iron-diene-complexes-relevant-to-catalytic-2-2-cycloaddition-reactions
#30
JOURNAL ARTICLE
C Rose Kennedy, Hongyu Zhong, Matthew V Joannou, Paul J Chirik
The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E) -piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4 -piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1 H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e- complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32256276/b-c-6-f-5-3-catalyzed-%C3%AE-deuteration-of-bioactive-carbonyl-compounds-with-d-2-o
#31
JOURNAL ARTICLE
Yejin Chang, Tanner Myers, Masayuki Wasa
An efficient deuteration process of α -C-H bonds in various carbonyl-based pharmaceutical compounds has been developed. Catalytic reactions are initiated by the action of Lewis acidic B(C6 F5 )3 and D2 O, converting a drug molecule into the corresponding boron-enolate. Ensuing deuteration of the enolate by in situ-generated D2 O+ -H then results in the formation of α -deuterated bioactive carbonyl compounds with up to >98% deuterium incorporation.
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32256275/site-selective-nitrene-transfer-to-conjugated-olefins-directed-by-oxazoline-peptide-ligands
#32
JOURNAL ARTICLE
Golo Storch, Naudin van den Heuvel, Scott J Miller
Site-selective nitrene transfer to di- and polyene substrates has been achieved using designed peptide-embedded bioxazoline ligands capable of binding copper. In model 1,3-diene substrates, the olefinic position proximal to a directing group was selectively functionalized. Additional studies indicate that this selectivity stems from non-covalent substrate-catalyst interactions. The peptide-mediated nitrene transfer was also applied to polyene natural product retinol and selective proximal functionalization allowed access to a cis -pyrroline modified retinoid...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32165875/chemoselective-tertiary-c-h-hydroxylation-for-late-stage-functionalization-with-mn-pdp-chloroacetic-acid-catalysis
#33
JOURNAL ARTICLE
Rachel K Chambers, Jinpeng Zhao, Connor P Delaney, M Christina White
Aromatic and heterocyclic functionality are ubiquitous in pharmaceuticals. Herein, we disclose a new Mn(PDP)catalyst system using chloroacetic acid additive capable of chemoselectively oxidizing remote tertiary C( sp 3 )-H bonds in the presence of a broad range of aromatic and heterocyclic moieties. Although catalyst loadings can be lowered to 0.1 mol% under a Mn(PDP)/acetic acid system for aromatic and non-basic nitrogen heterocycle substrates, the Mn(PDP)/chloroacetic acid system generally affords 10-15% higher isolated yields on these substrates and is uniquely effective for remote C( sp 3 )-H hydroxylations in substrates housing basic nitrogen heterocycles...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/32063821/pd-biphephos-is-an-efficient-catalyst-for-the-pd-catalyzed-s-allylation-of-thiols-with-high-n-selectivity
#34
JOURNAL ARTICLE
Thomas Schlatzer, Hilmar Schröder, Melanie Trobe, Christian Lembacher-Fadum, Simon Stangl, Christoph Schlögl, Hansjörg Weber, Rolf Breinbauer
The Pd-catalyzed S -allylation of thiols with stable allylcarbonate and allylacetate reagents offers several advantages over established reactions for the formation of thioethers. We could demonstrate that Pd/BIPHEPHOS is a catalyst system which allows the transition metal-catalyzed S -allylation of thiols with excellent n -regioselectivity. Mechanistic studies showed that this reaction is reversible under the applied reaction conditions. The excellent functional group tolerance of this transformation was demonstrated with a broad variety of thiol nucleophiles (18 examples) and allyl substrates (9 examples), and could even be applied for the late-stage diversification of cephalosporins, which might find application in the synthesis of new antibiotics...
January 23, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/34084099/radical-polar-crossover-annulation-a-platform-for-accessing-polycyclic-cyclopropanes
#35
JOURNAL ARTICLE
John A Milligan, Kevin L Burns, Anthony V Le, Viktor C Polites, Zheng-Jun Wang, Gary A Molander, Christopher B Kelly
Photoredox-mediated radical/polar crossover (RPC) processes provide unique solutions to challenging annulations. Herein, we describe an approach to the cyclopropanation of olefins that are embedded within bicyclic scaffolds. Whereas these systems are notoriously recalcitrant toward classical cyclopropanation approaches, RPC cyclopropanation can be executed with ease, leading to polycarbocyclic and polyheterocyclic cyclopropanes. The cyclopropanation proceeds through a photoredox-enabled Giese-type radical addition followed by an intramolecular anionic substitution reaction on a neopentyl leaving group...
January 7, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/33071705/catalytic-reductions-without-external-hydrogen-gas-broad-scope-hydrogenations-with-tetrahydroxydiboron-and-a-tertiary-amine
#36
JOURNAL ARTICLE
Kirill A Korvinson, Hari K Akula, Casina T Malinchak, Dellamol Sebastian, Wei Wei, Tashrique A Khandaker, Magdalena R Andrzejewska, Barbara Zajc, Mahesh K Lakshman
Facile reduction of aryl halides with a combination of 5% Pd/C, B2 (OH)4 , and 4-methylmorpholine is reported. Aryl bromides, iodides, and chlorides were efficiently reduced. Aryl dihalides containing two different halogen atoms underwent selective reduction: I over Br and Cl, and Br over Cl. Beyond these, aryl triflates were efficiently reduced. This combination was broadly general, effectuating reductions of benzylic halides and ethers, alkenes, alkynes, aldehydes, and azides, as well as for N -Cbz deprotection...
January 7, 2020: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/31875866/old-concepts-new-application-additive-free-hydrogenation-of-nitriles-catalyzed-by-an-air-stable-alkyl-mn-i-complex
#37
JOURNAL ARTICLE
Stefan Weber, Luis F Veiros, Karl Kirchner
An efficient additive-free manganese-catalyzed hydrogenation of nitriles to primary amines with molecular hydrogen is described. The pre-catalyst, a well-defined bench-stable alkyl bisphosphine Mn(I) complex fac -[Mn(dpre)(CO)3 (CH3 )] (dpre=1,2-bis(di- n -propylphosphino)ethane), undergoes CO migratory insertion into the manganese-alkyl bond to form acyl complexes which upon hydrogenolysis yields the active coordinatively unsaturated Mn(I) hydride catalyst [Mn(dpre)(CO)2 (H)]. A range of aromatic and aliphatic nitriles were efficiently and selectively converted into primary amines in good to excellent yields...
December 3, 2019: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/31894182/biocatalytic-enantioselective-oxidation-of-sec-allylic-alcohols-with-flavin-dependent-oxidases
#38
JOURNAL ARTICLE
Somayyeh Gandomkar, Etta Jost, Doris Loidolt, Alexander Swoboda, Mathias Pickl, Wael Elaily, Bastian Daniel, Marco W Fraaije, Peter Macheroux, Wolfgang Kroutil
The oxidation of allylic alcohols is challenging to perform in a chemo- as well as stereo-selective fashion at the expense of molecular oxygen using conventional chemical protocols. Here, we report the identification of a library of flavin-dependent oxidases including variants of the berberine bridge enzyme (BBE) analogue from Arabidopsis thaliana ( At BBE15) and the 5-(hydroxymethyl)furfural oxidase (HMFO) and its variants (V465T, V465S, V465T/W466H and V367R/W466F) for the enantioselective oxidation of sec -allylic alcohols...
November 19, 2019: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/31680790/aldolase-catalyzed-asymmetric-synthesis-of-n-heterocycles-by-addition-of-simple-aliphatic-nucleophiles-to-aminoaldehydes
#39
JOURNAL ARTICLE
Raquel Roldán, Karel Hernández, Jesús Joglar, Jordi Bujons, Teodor Parella, Wolf-Dieter Fessner, Pere Clapés
Nitrogen heterocycles are structural motifs found in many bioactive natural products and of utmost importance in pharmaceutical drug development. In this work, a stereoselective synthesis of functionalized N-heterocycles was accomplished in two steps, comprising the biocatalytic aldol addition of ethanal and simple aliphatic ketones such as propanone, butanone, 3-pentanone, cyclobutanone, and cyclopentanone to N -Cbz-protected aminoaldehydes using engineered variants of d-fructose-6-phosphate aldolase from Escherichia coli (FSA) or 2-deoxy-d-ribose-5-phosphate aldolase from Thermotoga maritima (DERA Tma ) as catalysts...
June 6, 2019: Advanced Synthesis & Catalysis
https://read.qxmd.com/read/31598119/chemoenzymatic-synthesis-of-sialic-acid-derivatives-using-immobilized-n-acetylneuraminate-lyase-in-a-continuous-flow-reactor
#40
JOURNAL ARTICLE
Victor R L J Bloemendal, Sam J Moons, Jurriaan J A Heming, Mohamed Chayoua, Olaf Niesink, Jan C M van Hest, Thomas J Boltje, Floris P J T Rutjes
The synthesis of N -acetylneuraminic acid (Neu5Ac) derivatives is drawing more and more attention in glycobiology research because of the important role of sialic acids in e. g. cancer, bacterial, and healthy cells. Chemical preparation of these carbohydrates typically relies on multistep synthetic procedures leading to low overall yields. Herein we report a continuous flow process involving N -acetylneuraminate lyase (NAL) immobilized on Immobead 150P (Immobead-NAL) to prepare Neu5Ac derivatives. Batch experiments with Immobead-NAL showed equal activity as the native enzyme...
June 6, 2019: Advanced Synthesis & Catalysis
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