Advanced Synthesis and Catalysis
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Selective Oxidation of Amines to Aldehydes or Imines using Laccase‐Mediated Bio‐Oxidation Abstract An efficient and practical chemo‐enzymatic aerobic oxidation in water of benzylamines to obtain aldehydes or imines is described. Laccase from Trametes versicolor was chosen as biocatalyst, and TEMPO (radical 2,2,6,6‐tetramethylpiperidine 1‐oxyl) as mediator. A study on the pH dependence of the aqueous medium allowed us to realise a fine tuning on product selectivity. Under our optimized reaction conditions, the bio‐oxidation of a series of primary, secondary and cyclic amines has been achieved. magnified image
Advanced Synthesis and Catalysis - Tập 357 Số 8 - Trang 1840-1848 - 2015
Palladium‐Catalyzed Oxidative Heck‐Type Allylation of β,β‐Disubstituted Enones with Allyl Carbonates Abstract The palladium‐catalyzed oxidative Heck‐type allylation of β,β‐disubstituted enones, i.e., α‐oxoketene dithioacetals, was efficiently realized with allyl carbonates, providing a concise route to highly functionalized dienes. The present synthetic methodology utilizes the substrate activation strategy to activate the CH bond of β,β‐disubstituted enones by introduction of a 1,2‐dithiolane functionality to make the enone substrate highly polarized and thus increase its reactivity, demonstrating rare examples for transition metal‐catalyzed allylic substitution of ß,ß‐disubstituted enones through a Heck‐type allylation process. magnified image
Advanced Synthesis and Catalysis - Tập 356 Số 9 - Trang 2097-2102 - 2014
Glycosyl Azides – An Alternative Way to Disaccharides Abstract Glycosyl azides are shown to be efficient donors for β‐galactosidases, β‐glucosidases and α‐mannosidases. Only α‐galactosidases do not cleave the respective glycosyl azide 1 and, moreover, they exhibit competitive inhibition (especially α‐galactosidase from Talaromyces flavus ). High water solubility and ready synthesis of glycosyl azides enable transglycosylation reactions even with difficult acceptors like N ‐acetyl‐D ‐mannosamine in good yields. The versatility of glycosyl azides was demonstrated in the synthesis of five disaccharides – two of them are described for the first time. All the reactions were highly regioselective, yielding β(1→6) isomers. β‐Galactosidase from E. coli proved to have the best synthetic capabilities. The present study shows that glycosyl azides are a valuable alternative to common p ‐nitrophenyl glycoside donors and in many synthetic reactions.
Advanced Synthesis and Catalysis - Tập 349 Số 8-9 - Trang 1514-1520 - 2007
Synthesis of Pyrimidopyrimidinediones in a Deep Eutectic Reaction Mixture Abstract An efficient and general synthesis of hexahydropyrimidopyrimidinediones has been developed employing a low melting L ‐(+)‐tartaric acid‐dimethylurea mixture as reaction medium. The melt acts at the same time as solvent, catalyst and reactant. Functionalized hexahydropyrimidopyrimidinediones are obtained in good to excellent yields after simple work‐up.
Advanced Synthesis and Catalysis - Tập 354 Số 13 - Trang 2368-2372 - 2012
Efficient and Eco‐Friendly Process for the Synthesis of Bis(1<i>H</i>‐indol‐3‐yl)methanes using Ionic Liquids Abstract Indoles react smoothly with carbonyl compounds in 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim]BF4 ) or 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim]PF6 ) ionic liquids under mild reaction conditions to afford the corresponding bis‐indolylmethanes in excellent yields. These ionic liquids can be recovered and recycled in subsequent reactions without any apparent loss of activity.
Advanced Synthesis and Catalysis - Tập 345 Số 3 - Trang 349-352 - 2003
Stille Reactions with Tetraalkylstannanes and Phenyltrialkylstannanes in Low Melting Sugar‐Urea‐Salt Mixtures Abstract The transfer of simple alkyl groups in Stille reactions usually requires special solvents (HMPA) or certain organotin reagents (stannatranes, monoorganotin halides) to be efficient. Using low‐melting mixtures of sugar, urea and inorganic salt as solvent, a fast and efficient palladium‐catalyzed alkyl transfer with tetraalkyltin reagents was observed. The high polarity and nucleophilic character of the solvent melt promotes the reaction. Stille biaryl synthesis using electron‐poor and electron‐rich aryl bromides proceeds with quantitative yields in the sugar‐urea‐salt melt. Catalyst loading may be reduced to 0.001 mol % and the catalyst melt mixture remains active in several reaction cycles. Showing the same or improved performance for Stille reactions than organic solvents and allowing a very simple work up, sugar‐urea‐salt melts are a non‐toxic and cheap alternative reaction medium available in bulk quantities for the catalytic process.
Advanced Synthesis and Catalysis - Tập 348 Số 15 - Trang 2243-2247 - 2006
Chiral Brønsted Acid‐Catalyzed Enantioselective Friedel–Crafts Reaction of 4,7‐Dihydroindoles with Trifluoromethyl Ketones Abstract In the presence of chiral phosphoric acid, an enantioselective Friedel–Crafts reaction of 4,7‐dihydroindoles with aromatic trifluoromethyl ketones and ethyl 4,4,4‐trifluoroacetoacetate has been realized. A series of 2‐substituted 4,7‐dihydroindoles with a trifluoromethylated tertiary alcohol moiety were obtained in 45–95% yields with 60–93% ee . Furthermore, 2‐functionalized indole derivatives could be produced through a one‐pot process.
Advanced Synthesis and Catalysis - Tập 352 Số 16 - Trang 2773-2777 - 2010
Chiral Brønsted Acid‐Mediated Enantioselective Organocatalytic Three‐Component Reaction for the Construction of Trifluoromethyl‐Containing Molecules Abstract In combination with the advantages of organocatalysis, we have developed a highly enantioselective Friedel–Crafts aminoalkylation of indoles with imines generated in situ from trifluoroacetaldehyde methyl hemiacetal and aniline. Novel chiral trifluoromethyl‐containing compounds were obtained in high yields with excellent enantioselectivities. This methodology was further extended to difluoroacetaldehyde methyl hemiacetal to demonstrate the broad scope of substrates.
Advanced Synthesis and Catalysis - Tập 350 Số 10 - Trang 1457-1463 - 2008
Synthesis of Unsymmetrical Diorganyl Chalcogenides under Greener Conditions: Use of an Iodine/DMSO System, Solvent‐ and Metal‐Free Approach Abstract Herein, we report a greener iodine‐catalyzed protocol to access different types of unsymmetrical diorganyl chalcogenides. This new approach works in the absence of solvent and metal. The desired products were obtained in good to excellent yields using one equivalent of arylboronic acids, half an equivalent of various diorganyl dichalcogenides, iodine (10 mol%) as a catalyst and 2 equivalents of dimethyl sulfoxide (DMSO; as oxidant), with a reaction time of 10 min under microwave irradiation. magnified image
Advanced Synthesis and Catalysis - Tập 357 Số 7 - Trang 1446-1452 - 2015
Selective Hydrogenation for Fine Chemicals: Recent Trends and New Developments Abstract In this overview, recent trends and developments for the selective hydrogenation of multifunctional molecules are discussed and assessed from the point of view of fine chemicals synthesis. In a first part, the design and preparation of catalysts and ligands with interesting properties are summarized, particularly meant for the catalysis specialist. The following topics are described in some detail: How enantioselective homogeneous catalysts are designed and tested; new effective chiral monodentate phosphines; successful bidentate phosphines ligand families (with axially chiral biaryl‐ and ferrocenyl‐based backbones, new phospholanes and with stereogenic phosphorus); novel bidentate ligand families with P‐O and P‐N bonds; and oxazoline‐based ligands. A short overview on immobilized chiral complexes and of the toolbox of heterogeneous catalysis (bimetallic, colloidal and modified catalysts) concludes this chapter. In a second part, progress for selected catalytic transformations and generic selectivity problems is described, intended mainly for the organic chemist who has to solve specific synthetic problems. Emphasis is on the following topics: The enantioselective hydrogenation of olefins with various substitution patterns; the chemo‐ and enantioselective hydrogenation of ketones; the diastereo‐ and enantioselective hydrogenation of CN functions; the stereoselective hydrogenation of aromatic rings; chemoselectivity and hydroxylamine accumulation in the reduction of functionalized nitroarenes; chemoselectivity and new protecting groups for catalytic debenzylation; the mild hydrogenation of carboxylic acid derivatives; and the chemoselective hydrogenation of nitriles. In the last parts of the review, transfer hydrogenation and mechanistic issues are discussed, followed by a short conclusions and outlook paragraph.
Advanced Synthesis and Catalysis - Tập 345 Số 1-2 - Trang 103-151 - 2003
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