- Low-water-content diazomethane-d2 and its isotopic assay
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A multiple D2O-CH2N2 exchange followed by a final anhydrification with K2CO3 gave an alcohol-free low-water-content ether solution of CD2N2. Procedural improvements for the excha
- Strazzolini, Paolo,Giumanini, Angelo G.,Verardo, Giancarlo
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- A practical and highly efficient synthesis of α-(trimethylsilyl)-difluoro-acetates
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An efficient method for the gram scale preparation of α-(trimethylsilyl)difluoroacetates is described. The key step involves Mg(0)-promoted selective C-F bond cleavage of readily available trifluoroacetates.
- Amii,Kobayashi,Uneyama
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- Halogenation of fluorinated cyclic 1,3-dicarbonyl compounds: new aspects of synthetic application
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In order to elaborate on an approach towards 2-(fluoroacyl)phenols being the superior alternative to the conventional Fries-rearrangement based methodology, the behaviour of cyclic fluorinated 1,3-dicarbonyls in reactions with halogenating agents was examined. The synthetic relevance of the polyhalogenated compounds obtained was demonstrated by the synthesis of several new heterocycles. An aromatization via a halogenation-dehydrohalogenation sequence proved to be a rewarding synthetic route to 2-(fluoroacyl)phenols and previously unknown 3-(fluoroacyl)thiochromones. The structure of one of the synthesized compounds was confirmed by X-ray diffraction analysis.
- Sevenard, Dmitri V.,Vorobyev, Mikhail,Sosnovskikh, Vyacheslav Ya.,Wessel, Helma,Kazakova, Olesya,Vogel, Vera,Shevchenko, Nikolay E.,Nenajdenko, Valentine G.,Lork, Enno,R?schenthaler, Gerd-Volker
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experimental part
p. 7538 - 7552
(2009/12/06)
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- Erbium(III) triflate as an extremely active acylation catalyst
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Erbium(III) triflate is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides {Ac 2O, (EtCO)2O, [(CH3)3CO] 2O, Bz2O, and (CF3CO)2O} without isomerisation of chiral centres. Moreover, the catalyst can be easily recycled and reused without significant loss of activity.
- Procopio, Antonio,Dalpozzo, Renato,De Nino, Antonio,Maiuolo, Loredana,Russo, Beatrice,Sindona, Giovanni
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p. 1465 - 1470
(2007/10/03)
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- A new finding in selective Baeyer-Villiger oxidation of α-fluorinated ketones; a new and practical route for the synthesis of α-fluorinated esters
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α-Fluorinated esters were effectively prepared by the Baeyer-Villiger oxidation of α-fluorinated ketones with m-chloroperbenzoic acid (m-CPBA) under mild conditions. The yield of the esters was influenced by the choice of solvent, base, and substituent on the aryl group of the ketones. 4-Methoxyphenyl substituted fluoroketones were oxidized almost quantitatively with m-CPBA within 10 min to 12 h at room temperature using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a cosolvent with CH2Cl2 (1:1, v/v) and aqueous buffer (KH2PO4-NaOH, pH 7.6) as an additive base. The oxidation reaction rates of α-fluorinated ketones were higher than those of the corresponding non-fluorinated ketones. The fluorine atom at α-position of fluoromethyl aryl ketones enhanced the reactivity in the Baeyer-Villiger oxidation.
- Kobayashi, Satoru,Tanaka, Hiroaki,Amii, Hideki,Uneyama, Kenji
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p. 1547 - 1552
(2007/10/03)
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- Electron-withdrawing substituents decrease the electrophilicity of the carbonyl carbon. An investigation with the aid of 13C NMR chemical shifts, v(C=O) frequency values, charge densities, and isodesmic reactions to interprete substituent effects on reactivity
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13C NMR chemical shifts and v(C=O) frequencies have been measured for several series of phenyl-or acyl-substituted phenyl acetates and for acyl-substituted methyl acetates to investigate the substituent-induced changes in the electrophilic character of the carbonyl carbon. Charge density, bond order, and energy calculations have also been performed. The spectroscopic and charge density results indicate that opposite to the conventional thinking, electron-withdrawing substituents do not increase the electrophilicity of the carbonyl carbon but instead decrease it. On the other hand, reaction energies of the isodesmic reactions designed show that electron-withdrawing substituents destabilize the carbonyl derivatives investigated. So, a significant ground-state destabilization of carboxylic acid esters, and carbonyl compounds in general, due to the decreased resonance stabilization, is proposed as a novel concept to explain both the increase in their reactivity and the changes in the chemical shifts and carbonyl frequencies induced by electron-withdrawing substituents.
- Neuvonen, Helmi,Neuvonen, Kari,Koch, Andreas,Kleinpeter, Erich,Pasanen, Paavo
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p. 6995 - 7003
(2007/10/03)
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- ACID CATALYZED REARRANGEMENTS OF 4-METHYL-4-CYANOCYCLOHEXADIENONE
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Acid-catalyzed dienone-phenol rearrangement reactions of 4-methyl-4-cyanocyclohexadienone occur very slowly and give either fragmentation or methyl group migration, not cyano group migration, under non-nucleophilic strongly acidic conditions.
- Marx, John N.,Zuerker, Joe,Hahn, Young-sook Paik
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p. 1921 - 1924
(2007/10/02)
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- OXIDATION BY THE SALTS OF METALS. VII. PLUMBATION AND OXIDATIVE SUBSTITUTION OF AROMATIC COMPOUNDS IN THE LEAD TETRAACETATE-LITHIUM CHLORIDE SYSTEM IN THE PRESENCE OF PERFLUORINATED CARBOXYLIC ACIDS
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The oxidation of benzene and substituted benzenes PhX with electron-donating (X = CH3, OCH3) and electron-withdrawing (X = Hlg, CF3, NO2) substituents in the Pb(OAc)4-LiCl system was investigated in the presence of perfluorinated carboxylic acids RfCOOH (Rf = CF3, C6F13).The reaction leads to the plumbation, chlorination, and acyloxylation products.It was shown that the reactions take place through the formation of aryl derivatives of lead(IV) with the participation of mixed-ligand complexes of lead.The products from the plumbation of toluene (in C6F13COOH in the absence of lithium chloride) and benzotrifluoro were isolated.In trifluoroacetic acid these intermediates undergo intramolecular redox decomposition with ligand transfer.The halogenobenzenes and benzotrifluoride are oxidized selectively in the CF3COOH-Pb(IV)-LiCl system, giving the corresponding aryl chlorides with yields close to quantitative (80-90percent).
- Serguchev, Yu. A.,Davydova, V. G.,Makhon'kov, D. I.,Beletskaya, I. P.
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p. 1006 - 1011
(2007/10/02)
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- 2'Hydroxy tetrazole-5-carboxanilides and anti-allergic use thereof
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New tetrazole derivatives of the general formula: STR1 [wherein R1 represents a halogen atom, a straight- or branched-chain alkyl, alkoxy, alkylthio, alkylsulphinyl, alkylsulphonyl or alkylsulphamoyl group, each such group containing from 1 to 6 carbon atoms, a dialkylsulphamoyl, dialkylamino, or dialkylcarbamoyl group (wherein the two alkyl groups may be the same or different and each contains from 1 to 4 carbon atoms), a straight- or branched-chain alkanoyl, alkoxycarbonyl, alkoxycarbonylamino, alkylcarbamoyl or alkanoylamino group containing from 2 to 6 carbon atoms, a cycloalkylcarbonyl group containing from 3 to 8 carbon atoms in the cycloalkyl moiety, or a hydroxy, formyl, nitro, trifluoromethyl, trifluoroacetyl, aryl, benzyloxycarbonylamino, amino, sulphamoyl, cyano, tetrazol-5-yl, carboxy, carbamoyl, benzyloxy, aralkanoyl or aroyl group, or a group of the formula: (wherein R2 represents a hydrogen atom or a straight- or branched-chain alkyl group containing from 1 to 5 carbon atoms, an aryl, aralkyl or trifluoromethyl group, or a cycloalkyl group containing from 3 to 8 carbon atoms, and R3 represents a hydrogen atom, or a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms optionally substituted by a phenyl group, or represents an aryl group optionally substituted by one or more substituents selected from halogen atoms and straight- or branched-chain alkyl and alkoxy groups containing from 1 to 6 carbon atoms and hydroxy, trifluoromethyl and nitro groups), and m represents zero or an integer 1, 2 or 3, the substituents R1 being the same or different when m represents 2 or 3] possess pharmacological properties, in particular properties of value in the treatment of allergic conditions.
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- Selectivity of the Aromatic Plumbylation Reaction
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The plumbylation of toluene in dichloroacetic acid yields initially 5.4percent 2-, 1.8percent 3-, and 92.7percent 4-methylphenyllead(IV) dichloroacetates.The toluene to benzene rate ratio under these conditions is 59.9.The partial rate factors are oMef = 9.64, mMef = 3.21, pMef = 331.The plumbylation of toluene in trifluoroacetic acid yields aryl trifluoroacetates and biaryls.Analysis of these products suggest that the plumbylation reaction yields 17.9percent 2-, 3.2percent 3-, and 78.9percent 4-methylphenyllead (IV) trifluoroacetates in the initial step of the reaction.The toluene to benzene rate ratio is 114 under these conditions.The partial rate factors are oMef = 61.2, mMef = 10.8, and pMef = 540.These observations suggest that the plumbylation reaction is a typical electrophilic substitution and that the reaction is significantly more selective than thallation or mercuration.
- Stock, Leon M.,Wright, Terry L.
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p. 4645 - 4648
(2007/10/02)
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- PHOSPHORORGANISCHE VERBINDUNGEN 93 Zur Chemie optisch aktiver Phosphinigsaereamide
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Optically active ethyl-phenyl-phosphinous acid diethylamide 1 was treated with HCl, HBF4, alcohols, thiols, carboxylic acids, esters, anhydrides, acid chloride, compounds with the structure element P-Cl and secondary phosphines to give in each case a racemic mixture of the corresponding, previously described, reaction products.Reaction of optically active 1 with para-cresol, para-cresyltrifluoro-acetate or 2,2,2-trifluoro-ethyl-trifluoro-acetate gives the corresponding optically active ester of ethyl phenyl phosphinous acid under retention of configuration.
- Horner, Leopold,Jordan, Manfred
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p. 235 - 242
(2007/10/02)
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