- Aromatics to diquinanes: An expeditious synthesis of tetramethylbicyclo[3. 3.0]octane framework of ptychanolide
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An expeditious route to methyl-7-oxo-1,4,5,8-tetramethylbicyclo[3.3.0] octane-3-carboxylate from a simple aromatic precursor is described. Oxidative dearomatization of 2-hydroxymethyl-3,4,6-trimethylphenol into spiroepoxycyclohexa-2,4-dienone, its cycloaddition and triplet-sensitized 1,2-acyl shift, and stereochemical inversion are the key features of our methodology. Georg Thieme Verlag Stuttgart.
- Singh, Vishwakarma,Chandra, Girish,Mobin, Shaikh M.
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- Understanding the Regioselectivity of Aromatic Hydroxylation over Divanadium-Substituted γ-Keggin Polyoxotungstate
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The aromatic hydroxylation of pseudocumene (PC) with aqueous hydrogen peroxide catalyzed by the divanadium-substituted γ-Keggin polyoxotungstate TBA4[γ-PW10O38V2(μ-O)(μ-OH)] (TBA-1H, TBA = tetrabutylammonium) has been studied using kinetic modeling and DFT calculations. This reaction features high chemoselectivity and unusual regioselectivity, affording 2,4,5-trimethylphenol (TMP) as the main product. Then the computational study was extended to the analysis of the regioselectivity for other alkoxy- and alkylarene substrates. The protonation/deprotonation of TBA-1H in MeCN/tBuOH (1:1) was investigated by 31P NMR spectroscopy. Forms with different protonation states, [γ-PV2W10O40]5- (1), [γ-HPV2W10O40]4- (1H), and [γ-H2PV2W10O40]3- (1H2), have been identified, and the protonation equilibrium constants were estimated on the basis of the 31P NMR data. DFT calculations were used to investigate the oxygen transfer process from hydroperoxo species, [γ-PW10O38V2(μ-O)(μ-OOH)]4- (2) and [γ-PW10O38V2(μ-OH)(μ-OOH)]3- (2H), and peroxo complex [γ-PW10O38V2(μ-2:2-O2)]3- (3) toward the different positions in the aromatic ring of PC, anisole, and toluene substrates. Product, kinetic, and computational studies on the PC hydroxylation strongly support a mechanism of electrophilic oxygen atom transfer from peroxo complex 3 to the aromatic ring of PC. The kinetic modeling revealed that the contribution of 3 into the initial reaction rate is, on average, about 70%, but it may depend on the reaction conditions. DFT calculations showed that the steric hindrance exerted by peroxo complex 3 is responsible for the origin of the unusual regioselectivity observed in PC hydroxylation, while for anisole and toluene the regioselective para-hydroxylation is due to electronic preference during the oxygen transfer from the active peroxo species 3.
- Skobelev, Igor Y.,Evtushok, Vasiliy Yu.,Kholdeeva, Oxana A.,Maksimchuk, Nataliya V.,Maksimovskaya, Raisa I.,Ricart, Josep M.,Poblet, Josep M.,Carbó, Jorge J.
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- Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum
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The volatiles emitted by the ascomycetes Hypoxylon griseobrunneum and Hypoxylon macrocarpum (Hypoxylaceae, Xylariales) were collected by use of a closed-loop stripping apparatus (CLSA) and analysed by GC-MS. The main compound class of both species were polysubstituted benzene derivatives. Their structures could only be unambiguously determined by comparison to all isomers with different substitution patterns. The substitution pattern of the main compound from H. griseobrunneum, the new natural product 2,4,5-trimethylanisole, was explainable by a polyketide biosynthesis mechanism that was supported by a feeding experiment with (methyl-2H3)methionine.
- Rinkel, Jan,Babczyk, Alexander,Wang, Tao,Stadler, Marc,Dickschat, Jeroen S.
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p. 2974 - 2990
(2019/01/05)
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- An Enzymatic Route to α-Tocopherol Synthons: Aromatic Hydroxylation of Pseudocumene and Mesitylene with P450 BM3
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Aromatic hydroxylation of pseudocumene (1 a) and mesitylene (1 b) with P450 BM3 yields key phenolic building blocks for α-tocopherol synthesis. The P450 BM3 wild-type (WT) catalyzed selective aromatic hydroxylation of 1 b (94 %), whereas 1 a was hydroxylated to a large extent on benzylic positions (46–64 %). Site-saturation mutagenesis generated a new P450 BM3 mutant, herein named “variant M3” (R47S, Y51W, A330F, I401M), with significantly increased coupling efficiency (3- to 8-fold) and activity (75- to 230-fold) for the conversion of 1 a and 1 b. Additional π–π interactions introduced by mutation A330F improved not only productivity and coupling efficiency, but also selectivity toward aromatic hydroxylation of 1 a (61 to 75 %). Under continuous nicotinamide adenine dinucleotide phosphate recycling, the novel P450 BM3 variant M3 was able to produce the key tocopherol precursor trimethylhydroquinone (3 a; 35 % selectivity; 0.18 mg mL?1) directly from 1 a. In the case of 1 b, overoxidation leads to dearomatization and the formation of a valuable p-quinol synthon that can directly serve as an educt for the synthesis of 3 a. Detailed product pattern analysis, substrate docking, and mechanistic considerations support the hypothesis that 1 a binds in an inverted orientation in the active site of P450 BM3 WT, relative to P450 BM3 variant M3, to allow this change in chemoselectivity. This study provides an enzymatic route to key phenolic synthons for α-tocopherols and the first catalytic and mechanistic insights into direct aromatic hydroxylation and dearomatization of trimethylbenzenes with O2.
- Dennig, Alexander,Weingartner, Alexandra Maria,Kardashliev, Tsvetan,Müller, Christina Andrea,Tassano, Erika,Schürmann, Martin,Ruff, Anna Jo?lle,Schwaneberg, Ulrich
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p. 17981 - 17991
(2017/11/29)
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- Thermal hazard evaluation of cumene hydroperoxide-metal ion mixture using DSC, TAM III, and GC/MS
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Cumene hydroperoxide (CHP) is widely used in chemical processes, mainly as an initiator for the polymerization of acrylonitrile-butadiene-styrene. It is a typical organic peroxide and an explosive substance. It is susceptible to thermal decomposition and is readily affected by contamination; moreover, it has high thermal sensitivity. The reactor tank, transit storage vessel, and pipeline used for manufacturing and transporting this substance are made of metal. Metal containers used in chemical processes can be damaged through aging, wear, erosion, and corrosion; furthermore, the containers might release metal ions. In a metal pipeline, CHP may cause incompatibility reactions because of catalyzed exothermic reactions. This paper discusses and elucidates the potential thermal hazard of a mixture of CHP and an incompatible material's metal ions. Differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III) were employed to preliminarily explore and narrate the thermal hazard at the constant temperature environment. The substance was diluted and analyzed by using a gas chromatography spectrometer (GC) and gas chromatography/mass spectrometer (GC/MS) to determine the effect of thermal cracking and metal ions of CHP. The thermokinetic parameter values obtained from the experiments are discussed; the results can be used for designing an inherently safer process. As a result, the paper finds that the most hazards are in the reaction of CHP with Fe2+. When the metal release is exothermic in advance, the system temperature increases, even leading to uncontrollable levels, and the process may slip out of control.
- You, Mei-Li
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- Selective oxidation of pseudocumene and 2-methylnaphthalene with aqueous hydrogen peroxide catalyzed by γ-Keggin divanadium-substituted polyoxotungstate
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The catalytic performance of a γ-Keggin divanadium-substituted phosphotungstate, (Bu4N)4[γ-PW10O38V2(μ-O)(μ-OH)], has been evaluated in the selective oxidation of 1,2,4-trimethylbenzene (pseudocumene, PC) and 2-methylnaphthalene with the green oxidant, 35% aqueous hydrogen peroxide. Under conditions of H2O2 deficiency ([PC]/[H2O2] = 17-22), PC oxidation proceeded with unusually high chemo- and regioselectivity, producing exclusively 2,4,5-trimethylphenol (2,4,5-TMP) and 2,3,5-TMP in a molar ratio of 7.3/1 and a yield of 73% based on the oxidant. Isomeric 2,3,6-trimethylphenol was found in trace amounts. Under conditions of H2O2 excess ([H2O2]/[PC] = 8), 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, vitamin E key intermediate) formed with 41% selectivity at 41% substrate conversion. Atypical regioselectivity was also found in the oxidation of 2-methylnaphthalene which gave predominantly 6-methyl-1,4-naphthoquinone (6-MNQ) rather than isomeric 2-MNQ. The ratio between the isomers could be altered by varying the catalyst and oxidant amounts.
- Zalomaeva, Olga V.,Evtushok, Vasiliy Yu.,Maksimov, Gennadii M.,Kholdeeva, Oxana A.
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p. 210 - 216
(2015/09/01)
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- Efficient method for demethylation of aryl methyl ether using aliquat-336
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A rapid method for selective cleavage of aryl methylethers can be achieved in the presence of a protic acid and a catalytic amount of phase-transfer catalyst (Aliquat-336). Aliquat-336 accelerates the rate of reaction and affords the corresponding phenols in excellent to good yields on a wide variety of substrates. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.]
- Waghmode, Suresh B.,Mahale, Ganesh,Patil, Viraj P.,Renalson, Kartik,Singh, Dharmendra
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supporting information
p. 3272 - 3280
(2013/10/01)
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- Novel dienone-phenol type rearrangement of 4,4-disubstituted cyclohexadienone system using thiosilane
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Thiosilane and a catalytic amount of a Bronsted acid mediate the novel domino-type rearrangement reaction of the 4,4-disubstituted cyclohexadienones to produce the 3,4-disubstituted benzenethioethers; the key step is 1,2-addition of thiosilane to dienone.
- Wada, Yasufumi,Otani, Kouji,Endo, Noriko,Kita, Yasuyuki,Fujioka, Hiromichi
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supporting information; experimental part
p. 797 - 799
(2010/06/12)
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- Catalytic activity of a mordenite catalyst in alkylation of xylenols with methanol
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The catalytic activity of a palladium-containing mordenite catalyst in alkylation of 2,6-, 2,4-, 2,5-, 2,3-, 3,4-, and 3,5-xylenols with methanol was studied. The main and by-products of catalysis and the activity of the catalyst in synthesis of individual trimethylphenols were determined.
- Agaev,Madatzade
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p. 683 - 684
(2007/10/03)
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- OXIDATION OF PSEUDOCUMENE IN ACETIC ACID
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The oxidation of pseudocumene in the benzene nucleus can be effected in HOAc solutions by using inorganic oxidizing agents containing oxygen, such as NaNO3, heteropolyacids, O2, Na2S2O8, and H2O2, with Pd(OAc)2 as catalyst.Na2S2O8 and H2O2 are the most ef
- Kholdeeva, O. A.,Kozhevnikov, I.V.,Sidel'nikov, V. N.,Utkin, V. A.
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p. 1903 - 1907
(2007/10/02)
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- On Dien-Ketenes from o-Quinol-Acetates
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A detailed picture of the photochemistry of o-quinol-acetates is presented. (RS)-6-Acetoxy-6-methyl-, (RS)-6-acetoxy-2,6-dimethyl-, (RS)-6-acetoxy-5,6-dimethyl-, (RS)-6-acetoxy-2,4,6-trimethyl-, (RS)-6-acetoxy-2,3,4,6-tetramethyl-, and (RS)-6-acetoxy-2,3,4,5,6-pentamethyl-2,4-cyclohexadien-1-ones serve as representative educts.There are two separate main photochemical routes conveniently designated as 1(?*,n) or 3(?*,?) tracks.The latter may also be attained by sensitization and leads to phenols.The former, by α-cleavage furnishes dien-ketens as indispensable phototransients.Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced bicyclization stereoselectively furnishes bicyclohex-3-en-2-ones, and multi-step addition of protic nucleophiles stereoselectively gives 1,4-, 1,6- and/or 1,2-adducts.By X-ray analysis or NOE studies, the structure of isolated photoproducts is established.Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates.Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that migth be present.Substituents primarily exert an influence upon the population of the various conformers of the dien-keten.Solvents affect the rate of the divers reaction paths competing for the phototransient.Nucleophiles play more than a trivial role when adducts are formed.With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate - or more general from a linear conjugated cyclohexadienone - is now predictable.
- Quinkert, Gerhard,Kleiner, Erna,Freitag, Bernd-Juergen,Glenneberg, Juergen,Billhardt, Uta-Maria,et al.
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p. 469 - 537
(2007/10/02)
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- A Regiocontrolled Annulation Approach to Highly Substituted Aromatic Compounds
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The thermal combination of cyclobutenone derivatives with heterosubstituted acetylenes provides a regiocontrolled route to highly substitutted aromatic compounds
- Danheiser, Rick L.,Gee, Stephen K.
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p. 1672 - 1674
(2007/10/02)
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- Process for producing alkylphenols
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This invention relates to a process for producing alkylphenols by oxidation of alkyl-substituted aromatic aldehydes with hydrogen peroxide in the presence of hydrogen fluoride and hydrolysis thereof. More particularly, under the presence of hydrogen fluoride alkyl substituted aromatic aldehydes are oxidized and converted selectively to aromatic alkyl phenol formates by hydrogen peroxide, without converting to corresponding aromatic carboxylic acid. After the completion of the oxidizing reaction, the produced alkyl phenol formates are hydrolyzed to corresponding alkyl phenols at the time of removing the remaining hydrogen fluoride by distillation.
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