- High-Fidelity Dimerization of Xanthenyl Radicals and Dynamic Qualities of a Congested Ethane: Diethyl Dixanthenyl-9,9′-Dicarboxylate
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Exploration of the sterically-congested ethane diethyl dixanthenyl-9,9′-dicarboxylate has revealed the dynamic behavior arising from its congested C?C bond. Interlocking ‘geared’ substituents and favorable dispersion interactions around this bond result in a conformational preference for partially cofacial xanthene moieties both in solid state and as dilute solutions. The weak, centrally located C?C bond is 1.628 ? long and permits selective thermolysis to yield two carbon-centered ethyl xanthenyl-9-carboxylate radicals, which dimerize with high fidelity into the original sterically-congested ethane. Recombination of the radicals into this symmetrical head-to-head dimer is highly reproducible – by observing the equilibrium, the bond dissociation enthalpy was calculated to be 20.4 kcal ? mol?1. The substituents around the central carbon provide insufficient stabilization against oxygen, which consumes the radicals and unbalances the dimer-radical equilibrium.
- Dubrawski, Zachary,Gelfand, Benjamin S.,Hogan, David T.,Sutherland, Todd C.
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supporting information
(2021/12/23)
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- Tert-Butyl Nitrite-Mediated Synthesis of N-Nitrosoamides, Carboxylic Acids, Benzocoumarins, and Isocoumarins from Amides
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This work reports tert-butyl nitrite (TBN) as a multitask reagent for (1) the controlled synthesis of N-nitrosoamide from N-alkyl amides, (2) hydrolysis of N-methoxyamides to carboxylic acids, (3) metal- and oxidant-free benzocoumarin synthesis from ortho-aryl-N-methoxyamides via N-H, C-N, and C-H bond activation, and (4) isocoumarin synthesis using Ru(II)/PEG as a recyclable catalytic system via ortho-C-H activation and TBN as an oxygen source. The sequential functional group interconversion of amide to acid has also been examined using IR spectroscopic analysis. Additionally, this methodology is highly advantageous due to short reaction time, gram scale synthesis, and broad substrate scope.
- Yedage, Subhash L.,Bhanage, Bhalchandra M.
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p. 5769 - 5781
(2017/06/07)
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- Synthetic method of xanthene-9-formic acid
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The invention discloses a synthetic method of xanthene-9-formic acid, which belongs to the field of chemical synthesis. The method comprises the following steps: xanthone is taken as a raw material, then is reduced to xanthydrol under alkaline condition by zinc dust, then the xanthydrol is subjected to a halogenated reaction to obtain the halogenated xanthene, then under effect of a catalyst, a cyanidation reaction is generated to obtain 9-cyan xanthene, through alkali hydrolysis, organic impurity is removed through extraction of an organic solvent, a xanthene-9-formate aqueous solution is obtained, and a xanthene-9-formic acid product is obtained through a neutralization reaction. The method has the advantages of simple operation and safe technology, the xanthene-9-formic acid with high purity is obtained without refining, and the method is easy and effective for industrial production.
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Paragraph 0035; 0042; 0043; 0044; 0051; 0052
(2017/12/09)
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- Amyl nitrite-mediated conversion of aromatic and heteroaromatic primary amides to carboxylic acids
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A series of aromatic and heteroaromatic primary amides were converted directly to carboxylic acids by heating with amyl nitrite in acetic acid. Most conversions proceeded to give reasonable to excellent yields on a range of substrates containing various functional groups. This reagent system is thus applicable for the direct hydrolysis of a range of different primary carboxamides. The reaction with a phenolic aromatic substrate afforded two alternative nitration products as major outcomes, evidencing alternative reaction pathways resulting from the free phenolic OH.
- Potter, Garrett T.,Jayson, Gordon C.,Miller, Gavin J.,Gardiner, John M.
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supporting information
p. 5153 - 5156
(2015/08/19)
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- A stability-indicating proton nuclear magnetic resonance spectroscopic method for the analysis of propantheline bromide in pharmaceutical samples
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A rapid, specific and accurate proton nuclear magnetic resonance (1H NMR) spectroscopic method was developed for the simultaneous quantitative analysis of propantheline bromide and its degradation product, xanthanoic acid, in bulk materials and tablets. 1,3,5-Trinitrobenzene served as an internal standard and deuterochloroform was used as the solvent for the analytical samples. The quantities of propantheline bromide and xanthanoic acid were calculated on the basis of the integrals for signals of the methine proton of propantheline at 5.09 ppm, the methine proton of xanthanoic acid at 4.99 ppm, and the aromatic protons of the internal standard at 9.39 ppm. The accuracy of the method was established through the analysis of synthetic mixtures containing the parent compound, its degradation product and the internal standard. An excellent agreement was verified between the assay results and the quantities of the various compounds in the mixtures. The mean ± SD recovery values for propantheline bromide and xanthanoic acid from a set of 10 synthetic mixtures were 99.6 ± 0.8% and 98.9 ± 1.8%, respectively. The assay of 10 lots of commercial propantheline bromide tablets by 1H NMR spectroscopy indicated drug and degradate contents in the ranges 97.1-99.8% and 0.1-0.9%, respectively. In addition, the proposed analytical method was found suitable for detecting the formation of xanthanoic acid from propantheline bromide in aqueous media in concentrations below 0.1% of that of the parent compound.
- Hanna,Lau-Cam
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p. 700 - 703
(2007/10/03)
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- Esters of bi- and tricyclic amino alcohols and their use in pharmaceutical compositions
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The new compounds of formula (wherein A and Z are defined as explained in the specification) can be prepared by conventional methods; they are suitable as active substances for pharmaceutical compositions.
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- Triarylmethanes and 9-arylxanthenes as prototypes amphihydric compounds for relating the stabilities of cations, anions and radicals by C-H bond cleavage and electron transfer
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Thermodynamic stability properties of 11 p-substituted trityl and seven 9-phenylxanthyl carbocations are reported in sulfolane and of their conjugate carbanions in DMSO. The cations are compared by calorimetric heats of hydride transfer from cyanoborohydride ion, their first and second reduction potentials, their pK+Rs in aqueous sulfuric acid, 13C chemical shifts and free energies of methoxy exchange. Carbanions are compared by their heats and free energies (pKHA) of deprotonation and their first and second oxidation potentials. Radicals are compared by their oxidation and reduction potentials. Their bond dissociation energies are derived by alternative routes: from the carbocation and its reduction potential and from the carbanion and its oxidation potential. The various properties are correlated against each other and against appropriate Hammett-type substituent parameters. Correlations between the different measured properties reported here range from fair to excellent. Despite their importance as historic prototypes for the three trivalent oxidation states of carbon, trityl and xanthyl systems are atypical models for comparing transmission of electron demand in other series of carbocations, radicals or carbanions with significantly different structures. The 9-arylxanthyl series is especially poor because of its insensitivity to substituent effects. The effects of substituents on various properties which represent the stabilities of R+s correlate surprisingly well against those for corresponding R-s. Accordingly, compensating effects on the oxidation and reduction of a series of related R.s may lead to a nearly constant electron transfer energy and absolute hardness for the series. In contrast, the free energies for interconversion of the carbocations and carbanions which determine the gap between pKR+. and pKHA are very sensitive to structural change.
- Arnett, Edward M.,Flowers II, Robert A.,Ludwig, Richard T.,Meekhof, Alison E.,Walek, Stuart A.
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p. 499 - 513
(2007/10/03)
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- N-acyl sulfamic acid esters (or thioesters), N-acyl sulfonamides, and N-sulfonyl carbamic acid esters (or thioesters) as hypercholesterolemic agents
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The present invention is directed to compounds useful for the regulation of cholesterol of Formula I, methods for using them and pharmaceutical compositions thereof, STR1 wherein X and Y are oxygen, sulfur, or (CR'R")n wherein n is 1 to 4; R is hydrogen, alkyl, or benzyl; R1 and R2 are phenyl, substituted phenyl, naphthyl, substituted naphthyl, an aralkyl group, an alkyl chain, adamantyl, or a cycloalkyl group.
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- Substituted xanthenylidene enols. The importance of β-Ar-C=C conjugation in the stabilization of aryl-substituted enols
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9-Xanthenecarboxaldehyde (7a) and methyl (7b), mesityl (7c), 2,4,6-triisopropylphenyl (Tip) (7d), and tert-butyl (7e) 9-xanthenyl ketones were prepared and found to be ketonic in CDCl3. In DMSO-d6,7a, 7c, 7d, and diphenylacetaldehyde 16 are in rapid equilibrium with the enols 15a, 15c, 15d, and 17, respectively. Keto ? enol equilibrium constants, Kenol, were measured in DMSO-d6 at various temperatures. The values at 294 K are 7a (101) > 16 (5.06) > 7d (1.1) > 7c (0.48). The ΔH° values are -2.0 to -4.4 kcal mol-1, and the ΔS° values are -9.1 to -11.8 cal mol-1 K-1. From the decrease of δ(OH) values on increasing the temperature, the association constants, Kassoc, of the enols with DMSO-d6 and the derived ΔHassoc and ΔSassoc values were obtained. The qualitative rates of formation of the enol acetates in DMSO-pyridine/Ac2O follow the Kenol values. X-ray diffraction data for 7b, 7c, and 18c - the acetate of 15c - gave the Ar - C=C and Mes - CO dihedral angles and showed that the xanthenyl moiety had a butterfly conformation. Several triarylethanones PhCH(Ar1)COAr2 (Ar1 = Ph, Ar2 = Mes, Tip; Ar1 = Ar2 = Mes) also isomerize in DMSO-d6 to the ketone-enol mixtures. The increase of Kenol by planarization of the β-aryl groups is reflected by the Kenol(7a)/Kenol(16) ratio of 20 at 294 K. Lower ratios for the α-aryl derivatives are Kenol(15c)/Kenol(Ph2CHCOMes) = 2 and 13.2 for the α-Tip analogues. These ratios were discussed in terms of ArC=C and ArC=O conjugation in the enols and ketones. β,β-Dimesityl substitution increased Kenol more than did β,β-diphenyl substitution due to steric effects. α-Alkyl substitution decreased Kenol strongly due to the higher stability of the ketones. The Kenol(DMSO-d6)/Kenol(H2O) ratio was 46 for 16 at 294 K. This first such ratio measured for a simple enol is ascribed to higher hydrogen bond acceptance by the DMSO-d6. Solvation of the enol is an important contributor to Kenol. The thermodynamic parameters resemble those for the nonsimple stable enol of acetylacetone rather than for the simple but much less stable enol, H2C=C(OH)Me.
- Rochlin, Elimelech,Rappoport, Zvi
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p. 230 - 241
(2007/10/02)
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- The Carboxylation of Active Methylene Compounds with Carbon Dioxide in the Presence of Diphenylcarbodiimide and Potassium Carbonate
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Active methylene compounds were effectively carboxylated with carbon dioxide in the presence of diphenylcarbodiimide (DPC) as a biotin model and potassium carbonate.Fluorene was carboxylated even under a nitrogen atmosphere in the presence of DPC, indicating that a carbonate ion was the carbon source.The reaction occured even in the presence of water.It was considered that reaction intermediates are stable to water and that the concentration of the carbonate ion is important for carboxylation.
- Chiba, Koji,Tagaya, Hideyuki,Karasu, Masa,Ono, Tsuyoyuki,Hashimoto, Kazumi,Moriwaki, Yasusi
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p. 966 - 970
(2007/10/02)
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- The Carboxylation of Active Methylene Compounds with Diphenylcarbodiimide and Potassium Carbonate
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Active methylene compounds were carboxylated by employing the reagent system, diphenylcarbodiimide and potassium carbonate, in dimethyl sulfoxide at room temperature and atmospheric pressure.The reaction proceeded even in the absence of carbon dioxide, but the carboxylation easily proceeded in carbon dioxide atmosphere.
- Chiba, Koji,Tagaya, Hideyuki,Karasu, Masa,Ono, Tsuyoyuki,Kugiya, Masashi
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