- Catalytic Activation of Unstrained C(Aryl)-C(Alkyl) Bonds in 2,2′-Methylenediphenols
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Catalytic activation of unstrained and nonpolar C-C bonds remains a largely unmet challenge. Here, we describe our detailed efforts in developing a rhodium-catalyzed hydrogenolysis of unstrained C(aryl)-C(alkyl) bonds in 2,2′-methylenediphenols aided by removable directing groups. Good yields of the monophenol products are obtained with tolerating a wide range of functional groups. In addition, the reaction is scalable, and the catalyst loading can be reduced to as low as 0.5 mol %. Moreover, this method proves to be effective to cleave C(aryl)-C(alkyl) linkages in both models of phenolic resins and commercial novolacs resins. Finally, detailed experimental and computational mechanistic studies show that with C-H activation being a competitive but reversible off-cycle reaction, this transformation goes through a directed C(aryl)-C(alkyl) oxidative addition pathway.
- Dong, Guangbin,Ratchford, Benjamin L.,Xue, Yibin,Zhang, Rui,Zhu, Jun
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supporting information
p. 3242 - 3249
(2022/02/23)
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- Alkylation of Phenols with tert-Butanol Catalyzed by H-Form of Y Zeolites with a Hierarchical Porous Structure
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tert-Butyl-substituted phenols have been synthesized via the reaction of phenol, o-, m-, and p-cresols with tert-butanol under the action of CBr4-promoted Y-zeolites in the H-form with a hierarchical porous structure.
- Bayguzina,Makhiyanova,Khazipova,Khusnutdinov
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p. 1554 - 1559
(2019/10/14)
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- Formal Asymmetric Cycloaddition of Activated α,β-Unsaturated Ketones with α-Diazomethylphosphonate Mediated by a Chiral Silver SPINOL Phosphate Catalyst
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An efficient method for preparing highly functionalized chiral nonspiro-phosphonylpyrazolines via an asymmetric formal 1,3-dipolar cycloaddition reaction of α-diazomethylphosphonate with activated, acyclic α,β-unsaturated ketones, bearing an additional nitrile electron-withdrawing group, has been developed, utilizing an in situ generated chiral silver phosphate catalyst, affording excellent stereoselectivities (up to 98% ee, 99:1 dr) and yields (up to 95%). A stepwise mechanism is proposed based upon density functional M11 calculations.
- Zheng, Bo,Chen, Haohua,Zhu, Lei,Hou, Xiqiang,Wang, Yan,Lan, Yu,Peng, Yungui
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supporting information
p. 593 - 597
(2019/01/21)
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- MCM-41-supported phosphotungstic acid-catalyzed cleavage of C-O bond in allyl aryl ethers
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Removal of the protecting allyl group from allyl aryl ethers in the presence of other oxygen protecting groups was successfully achieved using a solid acid supported on the high surface area material MCM-41. The catalyst showed excellent activity in the presence of various electron withdrawing, electron donating, and oxidizable functional groups. The methodology is also very useful for the removal of protecting allyl groups of various natural products such as vanillin, isovanillin, and other oxygen functionalized aldehydes and ketones.
- Sakate, Sachin S.,Kamble, Sumit B.,Chikate, Rajeev C.,Rode, Chandrashekhar V.
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p. 4943 - 4949
(2017/07/12)
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- Diastereofacial selectivity in reactions of substituted cyclohexyl radicals. An experimental and theoretical study
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The diastereofacial selectivity in reactions of a series of alkyl-substituted cyclohexyl radicals has been investigated. In additions of cyclohexyl radicals to alkenes, it has been found that only substituents bound at the olefinic center being attacked by the radical influence the equatorial-axial selectivity. Substituents bound to the radical center or axial substituents β to the radical center lead to increased axial attack. Equatorial β-substituents or axial γ-substituents increase the amount of equatorial attack. The same trends are observed for halogen and hydrogen abstraction reactions; the amount of axial reaction product is usually somewhat higher than in the addition reactions. The stereoselectivities can be explained with steric and torsional effects very similar to those suggested for nucleophilic addition reactions to cyclohexanones. A MM2 force field has been parameterized to gain further insight into the stereochemistry of the reaction.
- Damm,Giese,Hartung,Hasskerl,Houk,Hüter,Zipse
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p. 4067 - 4079
(2007/10/02)
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- EQULIBRATION OF TERT-ALKYLPHENOLS (THERMODYNAMIC ANALYSIS OF THE ALKYLATION OF PHENOLS USING BRANCHED-CHAIN OLEFINS).
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The authors describe the results of a study to evaluate the thermodynamic properties of t-Alk PHI ; these results; combined with earlier results, have enabled the authors to complete a thermodynamic analysis of the process for preparing tertiary alkylphenols.
- Nesterova,Verevkin,Malova,Pil'shchikov
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p. 748 - 754
(2007/10/02)
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- Trans-substitution and equilibration of phenols. Part IV. The influence of various catalysts on the trans-tert-butylation reaction of phenols; mechanistic aspects
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The trans-tert-butylation reaction by 2,6-di-tert-butyl-4-methylphenol has been studied for a number of phenols in the presence of different catalysts.Equilibria, as well as reaction kinetics, have been investigated.The mechanism involves the intermediacy of a tert-butyl ether.This mechanism is supported both by the kinetics and the initially high ortho/para ratio as well as by the reversed substituent effect.
- Willemse, F. R. J.,Kooyman, E. C.,Lamoen, H. B. van,Vos, D. de,Wolters, J.
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p. 206 - 209
(2007/10/02)
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- Electrophilic Substitution with Rearrangement. Part 10. Some Products of Bromination of 2,4-Dimethylphenol and of 4-t-Butyl-2-methylphenol
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The reaction of 2,4-dimethylphenol with bromine gives first 6-bromo-2,4-dimethylphenol, which according to the conditions of further bromination can give 4,6-dibromo-2,4-dimethylcyclohexa-2,5-dienone; a mixture of 5,6- with some 3,6-dibromo-2,4-dimethylphenol; 6-bromo-4-bromomethyl-2-methylphenol with none of the 2-bromomethyl-4-methyl isomer; or a mixture from which 6-bromo-2,4-bis(bromomethyl)phenol can be isolated.The corresponding dienone from 6-bromo-4-t-butyl-2-methylphenol reacts by more complex pathways, and the products include those of de-t-butylation.The probable mechanisms involved in these reactions are discussed.
- Brittain, Judith M.,Mare, Peter B. D. de la,Newman, Paul A.,Chin, Wong See
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p. 1193 - 1198
(2007/10/02)
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