- Facile and highly selective monoacylation of symmetric diols adsorbed on silica gel with acetyl chloride
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Monoacetylated alcohols of symmetric 1,n-diols are synthesized quantitatively by refluxing a suspension of the diols adsorbed on silica gel with acetylchloride.
- Ogawa, Haruo,Amano, Misa,Chihara, Teiji
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- Beneficial participation of the polymer: Improvement in polymer- supported oligosaccharide synthesis
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The reagent combination scandium(III) trifluoromethanesulfonate and acetic anhydride efficiently cleaves oligosaccharides bound to the polyethylene glycol (PEG) polymer-support via the dioxyxylene (DOX) linker. Unexpectedly, the site of cleavage is between the DOX linker and the PEG polymer. This method of cleavage allows for the use of DOX as a linker for synthesis on polystyrene-polyethylene glycol, PS-PEG beads.
- Mehta, Seema,Whitfield, Dennis
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- SYSTEM AND METHOD FOR PREPARING AROMATIC DERIVATIVE
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A system for preparing an aromatic derivative is provided, including: a photo-bromination reaction section for performing a photocatalytic reaction of an aromatic hydrocarbon and a brominating agent to form an aromatic hydrocarbon bromide; a substitution reaction section for performing a substitution reaction of the an aromatic hydrocarbon bromide from the photo-bromination reaction section with an alkali base compound or an alkali carboxylate compound to form an aromatic derivative; and a regeneration unit for reacting an alkali metal bromide formed by the substitution reaction section with an acid to form a hydrobromic acid. The regeneration unit is in fluid communication with the photo-bromination reaction section, such that the hydrobromic acid is recycled to the photo-bromination reaction section. A method for preparing the aromatic derivative is also provided.
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- Large-scale synthesis of a substituted d -phenylalanine using asymmetric hydrogenation
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A synthetic route to an N-BOC d-phenylalanine pharmaceutical intermediate suitable for rapid scale-up to 150-kg scale was required. A seven-step route based on asymmetric hydrogenation of an N-acetyl dehydroamino-acid was developed. Starting with terephthalic dialdehyde, monoreduction of one aldehyde group, Erlenmeyer condensation, and ring-opening/O-deacetylation with methanol provided the 4-(hydroxymethyl)-substituted dehydrophenylalanine hydrogenation substrate. Asymmetric hydrogenation of this enamide using [((R,R)-Ethyl-DuPhos) Rh(COD)BF4 proceeded in high enantiomeric excess. Subsequently, the cis-2,6-piperidyl group was introduced by mesylation/displacement, the BOC group was introduced, and acetyl and methyl ester groups were removed by basic hydrolysis. This route was used to manufacture 150 kg of the BOC amino acid 1.
- Fox, Martin E.,Jackson, Mark,Meek, Graham,Willets, Matthew
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experimental part
p. 1163 - 1171
(2012/01/05)
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- Desilylation-acetylation of trimethylsilyl ethers with acetic anhydride catalysed by montmorillonite K-10
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Two mild and simple one-step desilylation-acetylations of a variety of alkyl- and aryl-trimethylsilyl ethers, Me3SiOR(Ar), with acetic anhydride in the presence of montmorillonite K-10 clay are described.
- Movassagh,Lakouraj,Fasihi
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p. 348 - 349
(2007/10/03)
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- Anodic Oxidation of α-Substituted p-Xylenes. Electronic and Stereoelectronic Effects of α-Substituents in the Deprotonation of Alkylaromatic Radical Cations
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The effect of α-substituents on the deprotonation rate from the benzylic position of alkylaromatic radical cations, k(CH2Z)/k(CH3), has been investigated by determining the intramolecular selectivity in the anodic oxidation in acetic acid of a α-Z-substituted p-xylenes 1 (Z = H, OMe, OH, Me, tert-butyl, OAc, COOMe, CN), 5,6-dimethylindan 4 (R = H), and 2,2,5,6-tetramethylindan 4 (R = Me).Some oxidations induced by CAN have also been carried out.It has been found that, with the exception of when Z = tert-butyl, the deprotonation rate of 1.+ is always faster from the CH2Z group than from the CH3 group, independently of the electron-donating or electron-withdrawing nature of Z.The electron-donating groups (OH, OMe, Me), however, exert a larger effect than the electron-withdrawing ones (COOMe, CN).The negligible deprotonation rate from CH2-t-Bu has been ascribed to stereoelectronic effects (the bulky tert-butyl group does not allow the C-H bonds to be collinear with the ?-system), the suggestion being nicely confirmed by the observation that the deprotonation rate from the position 1(3), relative to that from the 5(6)-methyl group, is almost identical in the radical cations of 4 (R = H and Me).The effect of the other α-substituents is mainly of electronic nature and has been rationalized on the basis of a variable transition-state structure for the deprotonation process.It is suggested that with +R groups most of the charge, in the transition state, has been transferred to the Cα-H bond where it can be stabilized by the α-substituent.With electron-withdrawing groups less charge transfer has taken place and the rate-enhancing effects of these groups is ascribed to their capability to significantly decrease the strength of the Cα-H bond.
- Baciocchi, Enrico,Mattioli, Mario,Romano, Roberta,Ruzziconi, Renzo
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p. 7154 - 7160
(2007/10/02)
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- The Liquid-phase Oxidation of the Methylbenzenes by the Cobalt-Copper-Bromide System
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The liquid-phase oxidation of the methylbenzenes catalyzed by a catalyst system composed of cobalt(II) and copper(II) acetates and sodium bromide was carried out in the acetic acid at 150 deg C.The corresponding benzyl acetates and benzaldehydes were obtained in high selectivities in most cases.A nuclear-brominated product, i.e., 3-bromo-4-methoxytoluene was also obtained in the oxidation of p-methoxytoluene, wich has two different reaction sites, i.e., o-positions to the electron-donating methoxyl substituent and the benzyl position.However, the substitution of the bromide ion for the acetate ion in the catalyst system gave satisfactory selectivities for the side-chain oxidation products.In the p-xylene oxidation, α,α'-diacetoxy-p-xylene and p-(acetoxymethyl)benzoic acid were also obtained, as well as p-methylbenzyl acetate, though their amounts were small.The oxidation of polymethylbenzenes was also carried out.
- Okada, Toshihiko,Kamiya, Yoshio
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p. 2724 - 2727
(2007/10/02)
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- Electron-transfer Processes: Oxidation of Arylacetic Acids by Peroxydisulphate in Acetic Acid
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The oxidation of arylacetic acids by peroxydisulphate in acetic acid media in the presence of potassium and copper(II) acetates leads to the corresponding benzylacetates.The mechanism of the reaction is rationalized by the occurrence of two pathways: the intermediate formation of aromatic radical cations or the direct decarboxylation of the arylacetate ion.The importance of acetic acid as reaction medium is stressed.
- Giordano, Claudio,Beili, Aldo,Citterio, Attilio,Minisci, Francesco
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p. 1574 - 1576
(2007/10/02)
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