26191-64-0Relevant articles and documents
Preparation of metal-immobilized methacrylate-based monolithic columns for flow-through cross-coupling reactions
Sabarudin, Akhmad,Shu, Shin,Umemura, Tomonari,Yamamoto, Kazuhiro
, (2021/12/17)
With the aim of developing efficient flow-through microreactors for high-throughput organic synthesis, in this work, microreactors were fabricated by chemically immobilizing palladium-, nickel-, iron-, and copper-based catalysts onto ligand-modified poly(glycidyl methacrylate-co-ethylene dimethacrylate) [poly(GMA-co-EDMA)] monoliths, which were prepared inside a silicosteel tubing (10 cm long with an inner diameter of 1.0 mm) and modified with several ligands including 5-amino-1,10-phenanthroline (APHEN), iminodiacetic acid (IDA), and iminodimethyl phosphonic acid (IDP). The performance of the resulting microreactors in Suzuki?Miyaura cross-coupling reactions was evaluated, finding that the poly(GMA-co-EDMA) monolith chemically modified with 5-amino-1,10-phenanthroline as a binding site for the palladium catalyst provided an excellent flow-through performance, enabling highly efficient and rapid reactions with high product yields. Moreover, this monolithic microreactor maintained its good activity and efficiency during prolonged use.
The selective oxidation of substituted aromatic hydrocarbons and the observation of uncoupling via redox cycling during naphthalene oxidation by the CYP101B1 system
Hall, Emma A.,Sarkar, Md Raihan,Bell, Stephen G.
, p. 1537 - 1548 (2017/06/05)
The cytochrome P450 monooxygenase enzyme CYP101B1, from Novosphingobium aromaticivorans DSM12444, efficiently and selectively oxidised a range of naphthalene and biphenyl derivatives. Methyl substituted naphthalenes were better substrates than ethylnaphthalenes and naphthalene itself. The highest product formation activity for a singly substituted alkylnaphthalene was obtained with 2-methylnaphthalene. The oxidation of alkylnaphthalenes was regioselective for the benzylic methyl or methine C-H bonds. The products from 1- and 2-ethylnaphthalene oxidation were highly enantioselective with a single stereoisomer being generated in significant excess. The disubstituted substrate, 2,7-dimethylnaphthalene, had a higher product formation activity than either 1- and 2-methylnaphthalene. Methyl substituted biphenyls were also better substrates than biphenyl and had similar biocatalytic parameters to 1-methylnaphthalene. CYP101B1 catalysed oxidation of 2- and 3-methylbiphenyl was selective for attack at the methyl C-H bonds. The exception was the turnover of 4-methylbiphenyl which generated 4′-(4-methylphenyl)phenol as the major product (70%) with 4-biphenylmethanol making up the remainder. The drug molecule diclofenac was also regioselectively oxidised to 4′-hydroxydiclofenac by CYP101B1. The activity of the CYP101B1 system with naphthalene was more complex and the rate of NADH oxidation increased over time but very little product, 1-naphthol, was generated. Addition of samples of 1-naphthol and 2-naphthol and low concentrations of 1,4-naphthoquinone induced rapid NADH oxidation activity in the in vitro turnovers in both the presence and absence of the cytochrome P450 enzyme. Hydrogen peroxide was generated in these reactions in absence of the P450 enzymes demonstrating that the ferredoxin and ferredoxin reductase in combination with quinones from naphthol oxidation and oxygen can undergo redox cycling giving rise to a form of uncoupling of the reducing equivalents.
An alternative approach to para-C-H arylation of phenol: Palladium-catalyzed tandem γ-arylation/aromatization of 2-cyclohexen-1-one derivatives
Imahori, Tatsushi,Tokuda, Toru,Taguchi, Tatsuya,Takahata, Hiroki
supporting information; scheme or table, p. 1172 - 1175 (2012/04/04)
An efficient approach to prepare para-aryl phenols has been developed by using a Pd-catalyzed tandem γ-arylation/aromatization of 2-cyclohexen-1-one derivatives with aryl bromides. This approach provides various p-aryl phenols from the phenol surrogates, 2-cyclohexen-1-one derivatives, in a single reaction step on the basis of C-H arylation.
Multiple decomposition pathways for the oxenium ion precursor O-(4-(4′-methylphenyl)phenyl)-N-methanesulfonylhydroxylamine
Wang, Yue-Ting,Novak, Michael
body text, p. 7697 - 7706 (2010/03/01)
(Chemical Equation Presented) Although O-arylhydroxylamine derivatives have been claimed to be sources of oxeniumions in a large number of studies, it is not clear that the products of these reactions are due to oxenium ions. Previously, we had shown thro
Characterization of reactive intermediates generated during photolysis of 4-acetoxy-4-aryl-2,5-cyclohexadienones: Oxenium ions and aryloxy radicals
Wang, Yue-Ting,Jin, Kyoung Joo,Leopold, Samuel H.,Wang, Jin,Peng, Huo-Lei,Platz, Matthew S.,Xue, Jiadan,Phillips, David Lee,Glover, Stephen A.,Novak, Michael
experimental part, p. 16021 - 16030 (2009/05/16)
Aryloxenium ions 1 are reactive intermediates that are isoelectronic with the better known arylcarbenium and arylnitrenium ions. They are proposed to be involved in synthetically and industrially useful oxidation reactions of phenols. However, mechanistic studies of these intermediates are limited. Until recently, the lifetimes of these intermediates in solution and their reactivity patterns were unknown. Previously, the quinol esters 2 have been used to generate 1, which were indirectly detected by azide ion trapping to generate azide adducts 4 at the expense of quinols 3, during hydrolysis reactions in the dark. Laser flash photolysis (LFP) of 2b in the presence of O2 in aqueous solution leads to two reactive intermediates with γmax 360 and 460 nm, respectively, while in pure CH3CN only one species with λmax 350 nm is produced. The intermediate with Amax 460 nm was previously identified as lb based on direct observation of its decomposition kinetics in the presence of N3-, comparison to azide ion trapping results from the hydrolysis reactions, and photolysis reaction products (3b). The agreement between the calculated (B3LYP/6-31G(d)) and observed time-resolved resonance Raman (TR3) spectra of 1b further confirms its identity. The second intermediate with λ max 360 nm (350 nm in CH3CN) has been characterized as the radical 5b, based on its photolytic generation in the less polar CH 3CN and on isolated photolysis reaction products (6b and 7b). Only the radical intermediate 5b is generated by photolysis in CH3CN, so its UV-vis spectrum, reaction products, and decay kinetics can be investigated in this solvent without interference from 1b. In addition, the radical 5a was generated by LFP of 2a and was identified by comparison to a published UV-vis spectrum of authentic 5a obtained under similar conditions. The similarity of the UV-vis spectra of 5a and 5b, their reaction products, and the kinetics of their decay confirm the assigned structures. The lifetime of 1b in aqueous solution at room temperature is 170 ns. This intermediate decays with first-order kinetics. The radical intermediate 5b decomposes in a biphasic manner, with lifetimes of 12 and 75 μs. The decay processes of 5a and 5b were successfully modeled with a kinetic scheme that included reversible formation of a dimer. The scheme is similar to the kinetic models applied to describe the decay of other aryloxy radicals.
Mechanisms of the photochemical rearrangement of diphenyl ethers
Haga, Naoki,Takayanagi, Hiroaki
, p. 735 - 745 (2007/10/03)
The mechanism of the photochemical rearrangement of diphenyl ether (1a) was studied. Irradiation of 1a in ethanol gave 2-phenylphenol (2, 42%) and 4-phenylphenol (3, 11%) as rearrangement products, in addition to phenol (4, 30%) and benzene (5, 25%) as diffusion products. Cross-coupling experiments employing [2H10]1a demonstrated that the formation of 2- and 4-phenylphenol was an intramolecular process. Irradiation of 1a in benzene or in toluene gave biphenyls in good yields. The combined yields of rearrangement products (2 and 3) increased with increase of solvent viscosity, with a concomitant decrease in the formation of 4. All the results can be rationalized in terms of excitation of 1a to the singlet state and dissociation to a radical pair intermediate involving phenoxy and phenyl radicals. Intramolecular recombination of these radicals gives rearrangement products, and escape followed by hydrogen abstraction from the solvent gives diffusion products. When position 4 of 1a was occupied by an electron-donating substituent (1b-e), aryloxy-phenyl bond cleavage to give the corresponding rearrangement products prevailed over phenoxy-aryl bond cleavage. The opposite was the case for substrates with an electron-withdrawing substituent at position 4 (1h,i).
