- Catalytic Staudinger Reduction at Room Temperature
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We report an efficient catalytic Staudinger reduction at room temperature that enables the preparation of a structurally diverse set of amines from azides in excellent yields. The reaction is based on the use of catalytic amounts of triphenylphosphine as a phosphine source and diphenyldisiloxane as a reducing agent. Our catalytic Staudinger reduction exhibits a high chemoselectivity, as exemplified by reduction of azides over other common functionalities, including nitriles, alkenes, alkynes, esters, and ketones.
- Lenstra, Danny C.,Wolf, Joris J.,Mecinovi?, Jasmin
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p. 6536 - 6545
(2019/05/24)
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- Sustainable organophosphorus-catalysed Staudinger reduction
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A highly efficient and sustainable catalytic Staudinger reduction for the conversion of organic azides to amines in excellent yields has been developed. The reaction displays excellent functional group tolerance to functionalities that are otherwise prone to reduction, such as sulfones, esters, amides, ketones, nitriles, alkenes, and benzyl ethers. The green nature of the reaction is exemplified by the use of PMHS, CPME, and a lack of column chromatography.
- Lenstra, Danny C.,Lenting, Peter E.,Mecinovi?, Jasmin
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p. 4418 - 4422
(2018/10/17)
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- Production preparation method of p-nitrophenylethylamine hydrochloride
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The invention provides a production preparation method of p-nitrophenylethylamine hydrochloride, belongs to the technical field of drug synthesis, and solves the problems that in the prior art the synthetic p-nitrophenylethylamine hydrochloride is low in conversion rate of and is not suitable for large-scale industrial production. Synthesis steps include 1) amino protection, to be more specific, using beta-phenylethylamine as a raw material for reacting with an acyl protecting agent in a solvent to obtain an intermediate 1; 2) nitrating reaction, to be more specific, adding dropwise the intermediate 1 prepared by the step 1) into concentrated sulfuric acid, maintaining reaction temperature at room temperature, slowly adding dropwise concentrated nitric acid, after the completion of the reaction, adding crushed ice, adding an alkaline solution to adjust the pH to alkaline, and filtering to obtain an intermediate 2; and 3) deprotection, to be more specific, adding dropwise hydrochloric acid into the intermediate 2 in a solvent to adjust the pH to acid, heating to reflux, cooling, and precipitating the product p-nitrophenylethylamine hydrochloride. The production preparation method ofthe p-nitrophenylethylamine hydrochloride has low cost and high product yield, and is suitable for large-scale industrial production.
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Paragraph 0060; 0066; 0071
(2018/03/23)
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- Rapid Conventional and Microwave-Assisted Decarboxylation of L-Histidine and Other Amino Acids via Organocatalysis with R-Carvone under Superheated Conditions
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This article reports a new methodology taking advantage of superheated chemistry via either microwave or conventional heating for the facile decarboxylation of alpha amino acids using the recoverable organocatalyst, R-carvone. The decarboxylation of amino acids is an important synthetic route to biologically active amines, and traditional methods of amino acid decarboxylation are time consuming (taking up to several days in the case of L-histidine), are narrow in scope, and make use of toxic catalysts. Decarboxylations of amino acids including L-histidine occur in just minutes while replacing toxic catalysts with green catalyst, spearmint oil. Yields are comparable to or exceed previous methods and purification of product ammonium chloride salts is aided by an isomerization reaction of residual catalyst to phenolic carvacrol. The method has been shown to be effective for the decarboxylations of a range of natural, synthetic, and protected amino acids.
- Jackson, Douglas M.,Ashley, Robert L.,Brownfield, Callan B.,Morrison, Daniel R.,Morrison, Richard W.
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p. 2691 - 2700
(2015/12/18)
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- Substituent effects. 14. Anomalous dissociation constants in water-organic solvent mixtures: benzylammonium ions and related systems
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Thermodynamic dissociation constants in various water-organic solvent mixtures are given for benzylammonium, benzyldialkylammonium, and (2-phenylethyl)ammonium ions.Deviations from the Hammett equation (Eqn. 1) are similar to those observed for carboxylic acids, but of opposite sign.The extended Hammett equation (Eqn. 3), containing the hydrophobic constant, ?, yields good correlations.Derived secondary normal sigma values are exemplified.
- Hoefnagel, A. J.,Vos, R. H. de,Wepster, B. M.
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- Elimination Reactions of N-(2-(p-Nitrophenyl)ethyl)alkylammonium Ions by an E1cB Mechanism
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Elimination reactions of N-(2-(p-nitrophenyl)ethyl)quinuclidinium and 2-(p-nitrophenyl)ethyl)trimethylammonium ions catalyzed by hydroxide ion and buffer bases undergo a change in rate-determining step from an (E1cB)1 to an (E1cB)R mechanism with increasing buffer concentration in aqueous solution.Exchange of labeled 2H or 3H with solvent was shown for the quinuclidine and trimethylamine derivatives in the presence of buffers.Large inverse solvent deuterium isotope effects on the initial rate confirm the E1cB mechanism with leaving group expulsion partly or entirely rate determining under the same conditions.The dependence of log k on the pK of the leaving quinuclidine gives β1lg = -0.17 for k1 (proton abstraction), βp = 0.47 for k-1/k2 (partitioning of the intermediate zwitterion), and βlg = -0.64 for k1k2/k-1 (rate-determining expulsion of the leaving group).The ratio k2/k-1 increases from 10 to 59 with increasing ethanol concentration up to 40percent as the result of an increase in the rate of amine expulsion from the zwitterionic intermediate in the presence of organic cosolvents; k2/k-1 also increases with increasing temperature.Rate constants for elimination of 2-(p-nitrophenyl)ethyl halides increase with increasing leaving ability of the halide, consistent with a concerted E2 mechanism for all but the fluoride derivative.
- Keeffe, James R.,Jencks, William P.
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p. 265 - 279
(2007/10/02)
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