- Enantioselective Vanadium-Catalyzed Oxidative Coupling: Development and Mechanistic Insights
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The evolution of a more reactive chiral vanadium catalyst for enantioselective oxidative coupling of phenols is reported, ultimately resulting in a simple monomeric vanadium species combined with a Br?nsted or Lewis acid additive. The resultant vanadium complex is found to effect the asymmetric oxidative ortho-ortho coupling of simple phenols and 2-hydroxycarbazoles with good to excellent levels of enantioselectivity. Experimental and quantum mechanical studies of the mechanism indicate that the additives aggregate the vanadium monomers. In addition, a singlet to triplet crossover is implicated prior to carbon-carbon bond formation. The two lowest energy diastereomeric transition states leading to the enantiomeric products differ substantially with the path to the minor enantiomer involving greater torsional strain between the two phenol moieties.
- Kang, Houng,Herling, Madison R.,Niederer, Kyle A.,Lee, Young Eun,Vasu Govardhana Reddy, Peddiahgari,Dey, Sangeeta,Allen, Scott E.,Sung, Paul,Hewitt, Kirsten,Torruellas, Carilyn,Kim, Gina J.,Kozlowski, Marisa C.
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- Visible-Light-Driven di-t-Butyl Peroxide-Promoted the Oxidative Homo- and Cross-Coupling of Phenols
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The visible-light-induced oxidative homo- and cross-coupling of phenols by di-t-butyl peroxide (DTBP) are described. These reactions occur with metal-free process and feature high chemo- and regioselectivity under mild reaction conditions. DTBP is an inexpensive, benign, stable at room temperature, and commercially available oxidizer. It can be irradiated by blue LEDs to generate tert-butoxyl radical (tBuO?), which induces the oxidative homo-coupling of phenols and the cross-coupling of phenols with naphthols, respectively.
- Jia, Hanqiang,He, Min,Yang, Shilei,Yu, Xiaoqiang,Bao, Ming
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- Oxidative photocatalytic homo- And cross-coupling of phenols: Nonenzymatic, catalytic method for coupling tyrosine
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An oxidative photocatalytic method for phenol? phenol homo- and cross-coupling is described, and isolated yields of 16?97% are obtained. Measured oxidation potentials and computed nucleophilicity parameters support a mechanism of nucleophilic attack of one partner onto the oxidized neutral radical form of the other partner. Our understanding of this model permitted the development of cross-coupling reactions between nucleophilic phenols/arenes and easily oxidized phenols with high selectivity and efficiency. A highlight of this method is that one equivalent of each coupling partner is utilized. Building on these findings, a nonenzymatic, catalytic method for coupling tyrosine was also developed.
- Niederer, Kyle A.,Gilmartin, Philip H.,Kozlowski, Marisa C.
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p. 14615 - 14623
(2020/12/23)
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- Method for preparing 2-hydroxy-4-methyltetrahydropyran
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The invention relates to a method for preparing 2-hydroxy-4-methyltetrahydropyran (MHP) from using 3-methyl-3-buten-1-ol (IPEA) as a raw material under the catalysis of a rhodium compound and a tertiary phosphine ligand. After a reaction is finished, water extraction is performed for separating products from catalysts, wherein the rhodium catalyst and the tertiary phosphine ligand are reserved in an organic phase, the products are reserved in an aqueous phase, the conversion rate of IPEA can be as high as 99.7%, and the MHP selectivity of the products can be up tp 85.9%. The method solves the difficult problem that the costly rhodium catalyst is difficult to recover in a hydroformylation reaction process, and is favorable for industrial application.
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Paragraph 0059; 0063; 0064
(2017/07/21)
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- Solvent-Dependent Facile Synthesis of Diaryl Selenides and Biphenols Employing Selenium Dioxide
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Biphenols are important structure motifs for ligand systems in organic catalysis and are therefore included in the category of so-called "privileged ligands". We have developed a new synthetic pathway to construct these structures by the use of selenium dioxide, a stable, powerful, and commercially available oxidizer. Our new, and easy to perform protocol gives rise to biphenols and diaryl selenides depending on the solvent employed. Oxidative treatment of phenols in acetic acid yields the corresponding biphenols, whereas conversion in pyridine results in the preferred formation of diaryl selenides. As a consequence, we were able to isolate a broad scope of novel diaryl selenides, which could act as pincer-like ligands with further applications in organic synthesis or as ligands in transition metal catalysis.
- Quell, Thomas,Mirion, Michael,Schollmeyer, Dieter,Dyballa, Katrin M.,Franke, Robert,Waldvogel, Siegfried R.
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p. 115 - 119
(2016/05/02)
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- Selective oxidative homo-and cross-coupling of phenols with aerobic catalysts
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Simple catalysts that use atom-economical oxygen as the terminal oxidant to accomplish selective ortho-ortho, ortho-para, or para-para homo-couplings of phenols are described. In addition, chromium salen catalysts have been discovered as uniquely effective in the cross-coupling of different phenols with high chemo-and regioselectivity.
- Lee, Young Eun,Cao, Trung,Torruellas, Carilyn,Kozlowski, Marisa C.
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supporting information
p. 6782 - 6785
(2014/06/09)
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- Novel template-directed anodic phenol-coupling reaction
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Substituted phenols were anodically coupled to the corresponding 2,2'-biphenols via tetraphenoxy borate derivatives. This electrochemical method is particularly useful for methyl-substituted substrates, such as 2,4-dimethyl phenol. The selective ortho-coupling reaction can be easily performed on a multikilogram scale.
- Malkowsky, Itamar M.,Rommel, Christina E.,Froehlich, Roland,Griesbach, Ulrich,Puetter, Hermann,Waldvogel, Siegfried R.
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p. 7482 - 7488
(2007/10/03)
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