- CsOH catalyzed aerobic oxidative synthesis of p-quinols from multi-alkyl phenols under mild conditions
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p-Quinols are ubiquitous structural motifs of various natural products and pharmaceutical compounds, and versatile building blocks in synthetic chemistry. The reported methods for the synthesis of p-quinol require stoichiometric amounts of oxidants. Molecular oxygen is considered as an ideal oxidant due to its natural, inexpensive, and environmentally friendly characteristics. During the ongoing research of C-H bond hydroxylation, we found that multi-alkyl phenols could react with molecular oxygen under mild conditions. Herein, we describe an efficient oxidative de-aromatization of multi-alkyl phenols to p-quinols. 1 atm of molecular oxygen was used as the oxidant. Many multi-alkyl phenols could react smoothly at room temperature. Isotopic labeling experiment was also performed, and the result proved that the oxygen atom in the produced hydroxyl group is from molecular oxygen.
- Liang, Yu-Feng,Wu, Kai,Liu, Zhiqing,Wang, Xiaoyang,Liang, Yujie,Liu, Chenjiang,Jiao, Ning
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p. 1334 - 1339
(2015/03/18)
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- Solvolysis of 4-halogeno-4-alkyl-2,6-di-tert-butylcyclohexa-2,5-dienones induced by positive halogen donors as electrophiles
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Positive halogen donors such as N-iodosuccinimide (NIS) induce solvolysis of dienones 1, as model 4-halogenocyclohexa-2,5-dienones, in different hydroxylic solvents (ROH), yielding the 4-RO-cyclohexa-2,5-dienones (2). The rate of the solvolysis with NIS is highly dependent on the structure of ROH. The problem of such dependency is overcome by running the reaction in ROH diluted with MeCN, a polar aprotic solvent, in place of pure ROH; the rate of the reaction in the ROH-MeCN solvent mixture is almost independent of the structure (or the polarity) of ROH, and the reaction is completed faster or markedly faster than in neat ROH. The results suggest that the solvolysis rate is controlled by the polarity of the solvent system, although the hydrogen-bond acceptability of MeCN for dilution also accelerates the reaction. A mechanism for the solvolysis is proposed, involving electrophilic attack of a positive halogen donor at the halogen atom of 1, generating the 4-oxocyclohexa-2,5-dienyl cation intermediates (8) via the rate-limiting polar transition states. CSIRO 2013.
- Omura, Kanji
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p. 1386 - 1392
(2013/12/04)
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- Organo-peroxyl compounds via catalytic oxidation of a hindered phenol and aniline utilizing new manganese(II) bis benzimidazole diamide based complexes
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Bis benzimidazole diamide ligand-N,N′-bis(2-methylbenzimidazolyl) propanediamide [GBMA = L] has been synthesized and utilized to prepare new Mn(II) complexes of general composition [Mn(L)X2]·nH 2O where X is an exogenous anionic ligand(X = Cl-, CH 3COO-, SCN-). The geometry of the ligand and its Mn(II) complex have been optimized at the level of UHF, by using ZINDO/1 method. Binding energies, heat of formation and bond lengths of geometry optimized structures for the ligand and complex have been obtained. The oxidation of 2,4,6-tri-tert.-butylphenol (TTBP) and 2,4,6-tri-tert.-butylaniline (TTBA) has been investigated using these Mn(II) complexes as catalyst and TBHP as an alternate source of oxygen. The organo-peroxyl compounds have been isolated and characterized by 1H NMR, 13C NMR, IR and mass data. A different product profile was obtained when H2O2 is used as an oxidant.
- Bakshi, Ruchi,Mathur, Pavan
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experimental part
p. 3477 - 3488
(2011/02/15)
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- P-quinols and p-quinol Ethers from 2,4,6-trialkylphenols
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The oxidation of 2,4,6-trialkylphenols with lead(IV) oxide and 70% perchloric acid in water-acetone or in alcohols gives p-quinols or p-quinol ethers, respectively. Some nonmetallic oxidants serve the same purpose. Georg Thieme Verlag Stuttgart.
- Omura, Kanji
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experimental part
p. 208 - 210
(2010/03/03)
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- Electron transfer between protonated and unprotonated phenoxyl radicals
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(Chemical Equation Presented) The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO2 to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H2O containing an added acid provides eventually p-benzoquinone 39 and 4,4′-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.
- Omura, Kanji
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p. 858 - 867
(2008/09/19)
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- New insights into the reactivity of nitrogen dioxide with substituted phenols: A solvent effect
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Various alkyl-substituted phenols react readily with nitrogen dioxide (.NO2) in different solvents at room temperature. In all cases nitration is the major reaction and leads to the formation of mono- and dinitrophenols and 4-nitrocyclohexa-2,5-dienones from 2,4,6-tri-substituted phenols. Oxidation, dimerisation and, in one case, nitrosation are also observed. The reaction pathway followed changes according to the solvent and to the nature and the number of substituents on the phenolic ring. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Astolfi, Paola,Panagiotaki, Maria,Greci, Lucedio
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p. 3052 - 3059
(2007/10/03)
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- Reactivity and selectivity of aryloxylium ions
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The reactivity and selectivity of aryloxylium ions in acetonitrile-water mixtures are described. The 4-bromo-2,4,6-trialkylcyclohexa-2,5-dienones used as substrates were synthesised by electrophilic bromination in yields of 60% (3 R = Me) and 52% (7 R = B
- Hegarty, Anthony F.,Keogh, Joseph P.
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p. 758 - 762
(2007/10/03)
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- Synthesis and structure of 2,4,6-Tri-tert-butyl-4-hydroxy-2,5-cyclohexadienone
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2,4,6-Tri-tert-butyl-4-hydroxy-2,5-cyclohexadienone was synthesized by reaction of pentaphenyl-or penta-p-tolylantimony and 2,4,6-tri-tert-butylphenol in toluene in the presence of water. According to the X-ray diffraction data, the cyclohexadiene ring ad
- Sharutin,Sharutina,Osipov,Dorofeeva,Bel'skii
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p. 1254 - 1255
(2007/10/03)
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- A Simple and Efficient Procedure for the Preparation of p-Quinols by Hypervalent Iodine Oxidation of Phenols and Phenol Tripropylsilyl Ethers
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Oxidation of para-substituted phenols with benzene (BTIB) in aqueous acetonitrile at 0 deg C gives p-quinols in moderate to good yields; higher yields are obtained when tripropylsilyl ethers of phenols are used.
- McKillop, Alexander,McLaren, Lee,Taylor, Richard J. K.
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p. 2047 - 2048
(2007/10/02)
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- Free Radical Reactions of N-Heterocyclic Compounds. XIII. Oxidation of Cyclic Hydrazo Compounds with 2,4,6-Tri-tert-butyl-phenoxy Radical and Reactions of Radical Combination Products
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H-Heterocyclic compounds 1a,b containing the hydrazo structure were oxidized with 2,4,6-tri-tert-butyl-phenoxy radical (2).It was shown that the oxidation did not lead to the azo compounds 5a,b, but rather to radical combination products 6a,b of 2 via the intermediate hydrazyls 4a,b.The decomposition of adducts 6a,b was found to be similar to the reaction of radical combination products of aryl hydrazyls and CH-acidic compounds.The main reactions consisted of cleavage to starting radicals or elimination of isobutene forming the respective phenolic compounds 13a-c.
- Schulz, Manfred,Meske, Michael,Kluge, Ralph
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p. 350 - 354
(2007/10/02)
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- Catalytic Function of Cobalt(III) Complexes with N,N'-Disalicylideneethylenediamine on Oxygenation of t-Butylphenols
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Catalytic oxygenation of t-butylphenols has been examined with the cobalt(III) complexes with N,N'-disalicylideneethylenediamine (H2salen), K, Na, K, PF6, and PF6.The CO3-complex showed a high catalytic activity while the other complexes a low or no catalytic activity.Based on electronic and ESR spectral investigation, it has been shown that the reaction is initiated by the direct oxidation of t-butylphenols by the CO3-complex through a phenolatocobalt(III) intermediate.
- Aimoto, Yuko,Kanda, Wakako,Meguro, Sadatoshi,Miyahara, Yuji
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p. 646 - 650
(2007/10/02)
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- Some Rearrangements of 2,4,6-Tri-t-butyl-4-nitrocyclohexa-2,5-dienone
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Rearrangement of 2,4,6-tri-t-butyl-4-nitrocyclohexa-2,5-dienone (20) in benzene gives the 4-hydroxy dienone (21) and the mono-de-t-butylated 1,2-benzoquinone (22).The rearrangement is not affected by the addition of mesitylene, but the phenol-coupling product (26) is formed in the presence of p-cresol, and the nitromethyl phenol (31) is formed when the nitro dienone (20) rearranges in the presence of 2,4,6-trimethylphenol (29).The rearrangements of the nitro dienone (20) in methanol are described.
- Hartshorn, Michael P.,Kennedy, James A.,Simpson, Richard W.,Vaughan, John,Wright, Graeme J.
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p. 735 - 743
(2007/10/02)
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- Cyclodienones. X. Reaction of Halo-cyclohexadien-1-ones with Phenols in the Presence of α-Picoline and Preparation of 4-Hydroxy- and 2-Hydroxyphenyl Aryl Ethers
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Reaction of 4-halocyclohexadienones such as 4-bromo-(1a), 4-chloro-2,4,6-tri-t-butyl-(1b), 2,4-dichloro-4,6-di-t-butyl-2,5-cyclohexadien-1-one, and 2,4-dichloro-2,6-di-t-butyl-3,5-cyclohexadien-1-one with phenols in the presence of α-picoline was carried out under various conditions.The reaction of 1a and 1b with phenols afforded the corresponding 2-aryloxy-4,6-di-t-butyl phenols together with various by-products.The AlCl3 catalyzed trans-t-butylation of 2-aroxy-4,6-di-t-butyl-phenols, which were obtained by the above reaction, afforded the corresponding 2-hydroxyphenyl aryl ethers.The similar reaction of 4-aroxy-2,4,6-tri-t-butyl-2,5-cyclohexadien-1-ones also afforded the corresponding 4-hydroxyphenyl aryl ethers.
- Tashiro, Masashi,Itoh, Takashi,Fukata, Gouki
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p. 416 - 420
(2007/10/02)
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- Oxidation of Phenols by Molecular Oxygen Catalysed by Transition Metal Complexes. Comparison between the Activity of Various Cobalt and Manganese Complexes and the Role of Peroxy Intermediates
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The oxidation reactions of hindered phenols by molecular oxygen catalysed by monomeric and polymeric cobalt-Schiff base complexes, cobalt and manganese porphyrins, and (pyridine)cobaloxime are described; the rate and selectivity of these reactions are very dependent on the catalyst and on the solvent.A new product has been isolated, 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienylperoxy(pyridine)cobaloxime, and was fully characterised by its elemental analysis and spectroscopic methods.The reactivity of peroxy compounds derived from 2,4,6-tri-t-butylphenol which are postulated as intermediates in the oxidation of this phenol has been studied.Thermal decomposition of 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienyl(pyridine)cobaloxime indicates that the formation of this complex from the phenol, O2, and (pyridine)cobaloxime(II) is reversible and that it is converted into 2,6-di-t-butyl-1,4-benzoquinone only in the presence of a proton source.The corresponding hydroperoxide is probably an intermediate in this transformation as its decomposition in the presence of the cobalt(II) or manganese(III) complexes yields the same final products as the overall oxidations.
- Frostin-Rio, Maryvonne,Pujol, Daniele,Bied-Charreton, Claude,Perree-Fauvet, Martine,Gaudemer, Alain
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p. 1971 - 1980
(2007/10/02)
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- OXYDATION SELECTIVE EN PARA DES PHENOLS PAR UN COMPLEXE CUIVRIQUE OXYDANT
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Oxidation of phenols by molecular oxygen in the presence of the μ-oxo cupric catalyst Cu4Cl4O2 (CH3CN)3 (A), can be selectively directed to give either oxidative coupling or para-hydroxylation (p-quinols or p-quinones) products by the choice of the (A)/(phenol) ratio.The mechanism is discussed and a -OH ligand transfer from CuII to the phenolic para position is proposed.
- Capdevielle, Patrice,Maumy, Michel
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p. 5611 - 5614
(2007/10/02)
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- Peroxy Esters. 9. Base- and Radical-Induced Decomposition of 1-Alkyl-3,5-di-tert-butyl-4-oxo-2,5-cyclohexadienyl 3,5-Di-tert-butyl-4-hydroxyperbenzoates
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The title peroxy esters 1, when deprotonated with t-BuOK in DMF to the corresponding phenolate anions, decompose even at -78 deg C to give compounds 2-10.These compounds result undoubtedly from homolysis of the peroxy bond in 1, indicating that the generation of a carbanion at the α-position of the acyl group in peroxy esters (via resonance in the present case) induces ready homolysis of the peroxy bond.The oxidation of 1 with one-electron oxidizing agents gives rise to the corresponding phenoxy radicals, which also induce homolysis of the peroxy bond.
- Nishinaga, Akira,Nakamura, Koichi,Matsuura, Teruo
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p. 3700 - 3703
(2007/10/02)
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- Peroxy Esters. 8. Base-Catalyzed Rearrangement of Peroxy Esters: Formation of Alkoxyacetic Acid Derivatives
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p-Peroxyquinol esters derived from base-catalyzed oxygenation of 4-alkyl-2,6-tert-butylphenols followed by Schotten-Baumann acylation undergo a novel base-catalyzed rearrangement with t-BuOK in N,N-dimethylformamide to give p-quinoxyacetic acid derivatives in excellent yield.The same base-catalyzed rearrangement was also observed with tert-butyl peroxy esters.The base-catalyzed reaction of peroxy esters depended strongly on the nature of the acyl group in the esters and the base used and is suggested to involve homolysis of the peroxy bond.
- Nishinaga, Akira,Nakamura, Koichi,Matsuura, Teruo
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p. 3696 - 3700
(2007/10/02)
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- PHOTOINDUCED ELECTRON TRANSFER OXIDATION - 1. 9,10-DICYANOANTHRACENE-SENSITIZED PHOTOOXIDATION OF HINDERED PHENOLS.
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9,10-Dicyanoanthracene (DCA)-sensitized photooxidation reactions of hindered phenols and catechols (I) proceed via the initial electron transfer from 1 to **1DCA. 4-Hydroperoxy-2,5-cyclohexadien-1-ones and 4-hydroxy-2,5-cyclohexadien-1-ones are obtained from 2,4,6-trialkyl-substituted phenols, and an o-benzoquinone and furanone derivatives are afforded from 3,5-di-t-butylcatechol.
- Futamura,Yamazaki,Ohta,Kamiya
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p. 3852 - 3855
(2007/10/02)
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- Regioselective Formation of Peroxyquinolatocobalt(III) Complexes in the Oxygenation of 2,6-DI-t-butylphenols Schiff-base Complexes
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The oxygenation of 2,6-di-t-butylphenols with five-co-ordinated cobalt(II) Schiff-base complexes in aprotic solvents, such as CH2Cl2, thf, and dmf (thf = tetrahydrofuran, dmf = dimethylformamide), has been found to result in regioselective formation of peroxyquinolatocobalt(III) complexes.The regioselectivity depends on the nature of the substituent at the 4-position of the phenol used: 4-alkyl-2,6-di-t-butylphenols(1) afford peroxy-p-quinolatocobalt(III) complexes, whereas peroxy-o-quinolato-complexes are formed from 4-aryl-2,6-di-t-butyl-phenols (4).The initiation of the oxygenation is hydrogen abstraction by superoxocobalt(III) species from the phenols to give the corresponding phenoxy-radicals (10).Rapid reduction of (10) with cobalt(II) species follows giving rise to a phenolatocobalt(III) complex intermediate, within which dioxygen is incorporated.The regioselectivity of the oxygenation is attributable to the formation of the phenolatocobalt(III) complex intermediate.Crystals of the peroxy-p-quinolatocobalt(III) complex (2a) are orthorombic, space group P212121, with a = 33.749(11), b = 11.844(5), c = 9.329(4) Angstroem, and Z = 4.The crystal structure has been refined from 3 018 diffractometer data to R = 0.067.
- Nishinaga, Akira,Tomita, Haruo,Nishizawa, Kanji,Matsuura, Teruo,Ooi, Shunichiro,Hirotsu, Ken
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p. 1504 - 1514
(2007/10/02)
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- Cyclodienones. 7. Preparation and Reduction of 1-(3,5-Di-tert-butyl-2-hydroxyphenyl)pyridinium Halides
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The reactions of 4-bromo- (1a) and 4-chloro-2,4,6-tri-tert-butyl-2,5-cyclohexadien-1-one (1b) with compounds such as pyridine (4a), α- (4b), β- (4c), and γ-picoline (4d), and 3,5-lutidine (4e) were carried out under various conditions to produce the corresponding 1-(3,5-di-tert-butyl-2-hydroxyphenyl)pyridinium halides (7) or their intramolecular salts (8).The reduction of 7 and 8 with NaBH4 in methanol afforded in good yields the corresponding tetrahydropyridine derivatives (21), which were reduced to o-piperidinophenols (22) by hydrogenation with Raney Ni (W2) catalyst in high yields.The reaction pathway of the formation of 7 is also discussed.
- Fukata, Gouki,Itoh, Takashi,Tashiro, Masashi
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p. 4454 - 4458
(2007/10/02)
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- CYCLOHEXADIENONES. 5. REACTION OF 4-HALO-2,4,6-TRI-t-BUTYL-2,5-CYCLOHEXADIEN-1-ONES WITH IMIDAZOLES
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Reactions of 4-bromo- (1a) and 4-chloro-2,4,6-tri-t-butyl-2,5-cyclohexadien-1-one (1b) with imidazole (6b), 1-methyl- (6a), 2-methyl- (6c), 4-methylimidazole (6d), benzimidazole (6e), and 2-methylbenzimidazole (6f) was carried out under various conditions.It was found in these reactions that many products such as the 1-(4-oxo-2,5-cyclohexadienyl)-, 1-(2-hydroxyphenyl)- and 1-(4-hydroxyphenyl)imidazoles were formed and that the type of the products depended upon the structures of imidazoles 6.
- Fukata, Gouki,Itoh, Takashi,Tashiro, Masashi
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p. 549 - 554
(2007/10/02)
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- OXYGENATION OF 2,6-DI-t-BUTYLPHENOLS WITH SUPEROXO Co(lll) COMPLEXES
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Superoxo Co(lll) complexes, *3 where X= Et3N(+) and (Ph3P)2N(+), mediate the dioxygen incorporation into 2,6-di-t-butylphenols (1) with the same regioselectivity as that in the base-catalyzed oxygenation of 1.The superoxo species acts as a base but is not incorporated into the substrate.
- Nishinaga, A.,Tomita, H.,Matsuura, T.
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p. 2833 - 2836
(2007/10/02)
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- MECHANISM OF SELECTIVE p-QUINOL FORMATION IN THE COBALT SCHIFF BASE COMPLEX-CATALYZED OXYGENATION OF 4-ALKYL-2,6-DI-t-BUTYLPHENOLS
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The selective formation of p-quinols in the Co(Salpr)-catalyzed oxygenation of 4-alkyl-2,6-di-t-butylphenols in MeOH has been found to involve the rate determining reduction of peroxy-p-quinolato Co(III) complex formed in the initial fast step.An ionic me
- Nishinaga, A.,Tomita, H.,Matsuura, T.
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p. 1261 - 1264
(2007/10/02)
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