- Acid-Catalyzed Rearrangements of the Epoxides of Hexamethylbicyclohepta-2,5-dienone
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Epoxy enone 1 rearranges in trifluoroacetic acid (TFA) at 0 deg C to hexamethyl-8-oxabicycloocta-3,6-dien-2-one (3).A mechanism involving initial protonation of the carbonyl oxygen of 1, cleavage of the C-C bond of the epoxide ring, and the intermediacy of a dicyclopropylcarbinyl-type carbocation intermediate is suggested and supported by deuterium labeling.Epoxy enone 2 rearranges in TFA at 0 deg C to give products containing the TFA moiety in a form not easily hydrolyzed by base.The products have a structure with a plane of symmetry and are thought to be stereoisomers containing a 7-norbornenone skeleton and an ortho ester type of moiety (5).A mechanism involving intramolecular trapping of a carbocation by neighboring trifluoroacetate is suggested to explain the results.Pyrolysis of 3 (500 deg C) gives pentamethylphenol.
- Hart, Harold,Chen, Sun-Mao,Lee, Shin
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Read Online
- Selective C-C bond cleavage of amides fused to 8-aminoquinoline controlled by a catalyst and an oxidant
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Herein, copper-catalyzed direct C-C bond cleavage of amides fused to 8-aminoquinoline as a directing group to form urea in the presence of amines and dioxygen is reported. Compared to the previous C-H aminations of amides via C-H activation, this reaction presents a catalyst and oxidant controlled C-C bond cleavage strategy that enables amidation through a radical process. CuBr/Ag2CO3/O2 shows the best catalytic result at 150 °C. A series of aryl and alkyl amides were compatible with this transformation. Notably, this method provided access to cyclohexanone, one of the most important industrial materials. The pathway of this reaction was investigated.
- Li, Sen,Jie, Kun,Yan, Wenjie,Pan, Qingjun,Zhang, Min,Wang, Yufeng,Fu, Zhengjiang,Guo, Shengmei,Cai, Hu
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supporting information
p. 13820 - 13823
(2020/11/18)
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- CYCLIC PEROXIDE OXIDATION OF AROMATIC COMPOUND PRODUCTION AND USE THEREOF
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The present invention provides a method for converting an aromatic hydrocarbon to a phenol by providing an aromatic hydrocarbon comprising one or more aromatic C-H bonds and one or more activated C-H bonds in a solvent; adding a phthaloyl peroxide to the solvent; converting the phthaloyl peroxide to a di-radical; contacting the di-radical with the one or more aromatic C-H bonds; oxidizing selectively one of the one or more aromatic C-H bonds in preference to the one or more activated C-H bonds; adding a hydroxyl group to the one of the one or more aromatic C-H bonds to form one or more phenols; and purifying the one or more phenols.
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Page/Page column 9; 10
(2014/10/15)
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- A protocol to generate phthaloyl peroxide in flow for the hydroxylation of arenes
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A flow protocol for the generation of phthaloyl peroxide has been developed. This process directly yields phthaloyl peroxide in high purity (>95%) and can be used to bypass the need to isolate and recrystallize phthaloyl peroxide, improving upon earlier batch procedures. The flow protocol for the formation of phthaloyl peroxide can be combined with arene hydroxylation reactions and provides a method for the consumption of peroxide as it is generated to minimize the accumulation of large quantities of peroxide.
- Eliasen, Anders M.,Thedford, Randal P.,Claussen, Karin R.,Yuan, Changxia,Siegel, Dionicio
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supporting information
p. 3628 - 3631
(2014/08/05)
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- Metal-free oxidation of aromatic carbon-hydrogen bonds through a reverse-rebound mechanism
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Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Bronsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity.
- Yuan, Changxia,Liang, Yong,Hernandez, Taylor,Berriochoa, Adrian,Houk, Kendall N.,Siegel, Dionicio
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p. 192 - 196
(2013/08/23)
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- Synthesis of polyalkylphenyl prop-2-ynoates and their flash vacuum pyrolysis to polyalkylcyclohepta[b]furan-2(2H)-ones
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A new method for the smooth and highly efficient preparation of polyalkylated aryl propiolates has been developed. It is based on the formation of the corresponding aryl carbonochloridates (cf Scheme 1 and Table 1) that react with sodium (or lithium) propiolate in THF at 25-65°, with intermediate generation of the mixed anhydrides of the arylcarbonic acids and prop-2-ynoic acid, which then decompose almost quantitatively into CO2 and the aryl propiolates (cf. Scheme 11). This procedure is superior to the transformation of propynoic acid into its difficult-to-handle acid chloride, which is then reacted with sodium (or lithium) arenolates. A number of the polyalkylated aryl propiolates were subjected to flash vacuum pyrolysis (FVP) at 600-650°and 10-2 Torr which led to the formation of the corresponding cyclohepta[b]furan-2(2H)-ones in average yields of 25-45% (cf. Scheme 14). It has further been found in pilot experiments that the polyalkylated cyclohepta[b]furan-2(2H)-ones react with 1-(pyrrolidin-1-yl)cyclohexene in toluene at 120-130°to yield the corresponding 1,2,3,4- tetrahydrobenz[a]azulenes, which become, with the growing number of Me groups at the seven-membered ring, more and more sensitive to oxidative destruction by air (cf. Scheme 15).
- Nagel, Matthias,Hansen, Hans-Juergen
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p. 1022 - 1048
(2007/10/03)
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- The Baeyer-Villiger Oxidation of Aromatic Aldehydes and Ketones with Hydrogen Peroxide Catalyzed by Selenium Compounds
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A series of organoselenium compounds was investigated as activators of hydrogen peroxide in the Baeyer-Villiger oxidation.As a result, a convenient and cheap method for transformation of aromatic aldehydes, having polycondensed ring systems or electron-donating substituents, and polymethoxy derivatives of acetophenone, into phenols was elaborated.This method utilizes hydrogen peroxide activated by areneseleninic acids, as oxidizing agent.
- Syper, Ludwik
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p. 167 - 172
(2007/10/02)
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- A quantitative examination of the photoisomerization of some protonated phenols
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The photoisomerization of a series of protonated, methyl substituted phenols to protonated bicyclohexenones has been examined.These reactions, which were carried out in CF3SO3H as a strong acid solvent at ambient temperatures, provide a convenient route to a variety of bicyclohexenones.The quantum yields for these photoisomerizations vary from 0.018 for protonated 3,5-dimethylphenol to 0.65 for protonated 2,6-dimethylphenol.This variation in efficiency can be understood in terms of a competition between ring opening, to regenerate the starting phenol, or cyclopropyl migration, to give product, of aninitially formed intermediate.
- Childs, Ronald F.,George, Baha E.
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p. 1343 - 1349
(2007/10/02)
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- Thermal isomerizations of protonated bicyclohexenones
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The thermal isomerizations of a wide range of protonated methyl substituted bicyclohex-3-en-2-ones to protonated phenols has been examined using triflic acid as a strong acid solvent.The rate constants and activation energies of these isomerization has been determined.The barriers to the isomerizations were shown to be dependent on the number and position of the methyl substituents.The results show that three different mechanisms are needed to account for these isomerizations, two of which involve a preliminary circumambulatory rearrangement prior to ring opening and the other process involving a direct ring opening of the initial protonated bicyclohexenone to give an intermediate meta-protonated phenol.
- Childs, Ronald F.,George, Baha E.
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p. 1350 - 1354
(2007/10/02)
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- REACTION OF 1,2,4-TRIMETHYLBENZENE WITH PERACETIC ACID
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The oxidation of 1,2,4-trimethylbenzene with peracetic acid leads to the formation of trimethylphenols and hydroquinones, which undergo transformations to the corresponding benzoquinones and products from oxidative cleavage of the ring.The controlling stage of the process is the electrophilic hydroxylation of 1,2,4-trimethylbenzene.
- Kharchuk, V. G.,Kolenko, I. P.,Petrov, L. A.,Gus'kova, L. M.
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p. 2071 - 2078
(2007/10/02)
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- ON THE PHOTOISOMERIZATION OF BICYCLODIENONES
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Two bicyclodienones, which differ from one another only by the presence or absence of an O atom as the "n" bridge, show very different photoisomerization behavior.Irradiation of hexamethyl-8-oxabicyclooctadienone 12 gives endo-6-acetylpentamethylbicyclohexenone 16, probably via an initial sigmatropic rearrangement (Scheme 3).In contrast, hexamethylbicycloheptadienone 14 photoisomerizes via an initial -sigmatropic rearrangement, the isolated product being the relatively stable cyclopentadiene-ketene 26.The methylene analog of 14 (i.e.32) rearranges similarly, giving allene 33 and alkyne 34.The mechanisms of these photoisomerizations are discussed.
- Hart, Harold,Chen, Sun-Mao,Nitta, Makoto
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p. 3323 - 3328
(2007/10/02)
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- QUANTITATIVE DESCRIPTION OF REACTIONS OF AROMATIC COMPOUNDS WITH ELECTROPHILIC AGENTS. I. ELECTROPHILIC HYDROXYLATION OF METHYLBENZENES
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A scheme is proposed by means of which it is possible to assess the role of various reaction paths and the composition of the reaction products in terms of the theory of electrophilic hydroxylation of methylbenzenes by the initial addition of the electrophile at a ring carbon-carbon ? bond, controlled by charge and orbital factors, and the subsequent formation of isomeric ? complexes in ratios determined by their thermodynamic stability.
- Koptyug, V. A.,Rogozhnikova, O. Yu.,Detsina, A. N.
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p. 1193 - 1203
(2007/10/02)
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- Photorearrangements of Epoxy Ketones. Epoxides of Hexamethylbicyclohepta-2,5-dienone, a Valence Tautomer of Hexamethyltropone
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The double bond in the four-membered ring of hexamethylbicyclohepta-3,6-dien-2-one (1) is selectively oxidized by m-chloroperbenzoic acid, whereas the enone double bond is selectively epoxidized by alkaline hydrogen peroxide to give 2 and 3, respectively.In each case, a single stereoisomer is formed.The exo stereochemistry of the epoxides was deduced from X-ray structures on diepoxides 4 and 5 obtained by further epoxidation of 2 and 3.Irradiation of 2 gives pentamethylphenol (6) and ketene; if 2 is labeled at the C4 methyl with deuterium, the resulting 6 is labeled para to the hydroxyl group.A novel rearrangement of the four-membered ring to give a 7-norbornenyl-type intermediate is suggested to rationalize the labeling result.Irradiation of 3 gives, in addition to minor amounts of pentamethylphenol and its acetate, a tetracyclic product formulated as 10, which rearranges thermally to 1-acetylpentamethylcyclopentadiene (12).A mechanism involving photochemical C-C bond cleavage of the epoxide ring in 3 is suggested to account for the results.
- Hart, Harold,Chen, Sun-Mao,Lee, Shin,Ward, Donald L.,Kung, Wei-Jen Hu
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p. 2091 - 2096
(2007/10/02)
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- Light-induced Reactions, XIV. Rules for Determining Spectra of 2,4-Cyclohexadien-1-ones
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2,4-Cyclohexadien-1-ones of formula types 1 to 5 (cf.Fig. 1) provide basic values and positional increments for UV and 13C NMR spectra.These parameters allow to distinguish between constitutional isomers belonging to one and the same column of the graph of Fig. 1.It has become possible, e.g., to identify clearly the constitutional isomers 6 and 8 or 12 and 14, respectively.
- Quinkert, Gerhard,Duerner, Gerd,Kleiner, Erna,Adam, Friedhelm,Haupt, Erhard,Leibfritz, Dieter
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p. 2227 - 2248
(2007/10/02)
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- Alkylation process
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Substituted pyrrole compounds, such as 3-ethyl-4-methyl-5-carbethoxy pyrrole, 2,4-dimethyl-3-acetyl pyrrole and 2-methyl-5-carboxy pyrrole-4-propionic acid diethyl ester, are alkylated in a single step by reaction with an aldehyde or ketone in the presence of both an acid condensing agent such as hydriodic acid and a compatible reducing agent such as metallic zinc or stannous chloride. Suitable carbonyl reactants include formaldehyde, paraldehyde, isobutyraldehyde, acetone, cyclohexanone and methyl-isobutyl ketone. This application is a continuation application of U.S. application Ser. No. 281,624 filed Aug. 18, 1972, now abandoned, which is a continuation-in-part application of U.S. application Ser. No. 832,001, filed June 10, 1969, now abandoned.
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