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(Diacetoxyiodo)benzene-Mediated C-H Oxidation of Benzylic Acetals.

ABSTRACT: A useful oxidation of C-H bond of benzylic acetals has been achieved. This method avoids the use of stoichiometric metals and is compatible with the presence of both electron-donating and electron-withdrawing substituents on the aromatic ring. Oxidation was carried out by rapid microwave irradiation of benzylic acetals with PhI(OAc)2 as the oxidant. This led to the oxidation of acetals into 2-acetoxy-1,3-dioxolanes. Furthermore, this transformation protocol encompasses a wide range of valuable conversions of these useful synthons into different carboxylic acid derivatives.

SUBMITTER: Aman H

PROVIDER: S-EPMC6964519 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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(Diacetoxyiodo)benzene-Mediated C-H Oxidation of Benzylic Acetals.

Aman Hasil H Wang Yen-Hsiang YH Chuang Gary Jing GJ

ACS omega 20191230 1

A useful oxidation of C-H bond of benzylic acetals has been achieved. This method avoids the use of stoichiometric metals and is compatible with the presence of both electron-donating and electron-withdrawing substituents on the aromatic ring. Oxidation was carried out by rapid microwave irradiation of benzylic acetals with PhI(OAc)<sub>2</sub> as the oxidant. This led to the oxidation of acetals into 2-acetoxy-1,3-dioxolanes. Furthermore, this transformation protocol encompasses a wide range of ...[more]

PMID: 31956846

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Project description:Iodosilarene derivatives (PhIO, PhI(OAc)2) constitute an important class of oxygen atom transfer reagents in organic synthesis and are often used together with iron-based catalysts. Since the factors controlling the ability of iron centers to catalyze alkane hydroxylation are not yet fully understood, the aim of this report is to develop bioinspired non-heme iron catalysts in combination with PhI(OAc)2, which are suitable for performing C-H activation. Overall, this study provides insight into the iron-based ([FeII(PBI)3(CF3SO3)2] (1), where PBI = 2-(2-pyridyl)benzimidazole) catalytic and stoichiometric hydroxylation of triphenylmethane using PhI(OAc)2, highlighting the importance of reaction conditions including the effect of the co-ligands (para-substituted pyridines) and oxidants (para-substituted iodosylbenzene diacetates) on product yields and reaction kinetics. A number of mechanistic studies have been carried out on the mechanism of triphenylmethane hydroxylation, including C-H activation, supporting the reactive intermediate, and investigating the effects of equatorial co-ligands and coordinated oxidants. Strong evidence for the electrophilic nature of the reaction was observed based on competitive experiments, which included a Hammett correlation between the relative reaction rate (logkrel) and the σp (4R-Py and 4R'-PhI(OAc)2) parameters in both stoichiometric (ρ = +0.87 and +0.92) and catalytic (ρ = +0.97 and +0.77) reactions. The presence of [(PBI)2(4R-Py)FeIIIOIPh-4R']3+ intermediates, as well as the effect of co-ligands and coordinated oxidants, was supported by their spectral (UV-visible) and redox properties. It has been proven that the electrophilic nature of iron(III)-iodozilarene complexes is crucial in the oxidation reaction of triphenylmethane. The hydroxylation rates showed a linear correlation with the FeIII/FeII redox potentials (in the range of -350 mV and -524 mV), which suggests that the Lewis acidity and redox properties of the metal centers greatly influence the reactivity of the reactive intermediates.

Project description:Anaerobic activation of benzene is expected to represent a novel biochemistry of environmental significance but research into the mechanisms has been stymied by a lack of a genetically tractable pure culture which unequivocally does not use molecular oxygen to activate benzene. Geobacter metallireducens grew in a medium in which benzene was the sole electron donor and Fe(III) was the sole electron acceptor with a stoichiometry of benzene loss and Fe(III) reduction consistent with benzene oxidation to carbon dioxide coupled with Fe(III) reduction. Phenol labeled with 18O was produced when the medium was labeled with H218O, as expected for a true anaerobic conversion of benzene to phenol. Gene expression patterns indicated that benzene was metabolized through a phenol intermediate rather than benzoate or toluene. Deletion of ppcB, which encodes a subunit of the phenylphosphate carboxylase, an enzyme required for phenol metabolism, inhibited metabolism of benzene. Deleting genes specific for benzoate or toluene metabolism did not. Comparison of gene expression patterns in cells grown on benzene versus cells grown on phenol revealed genes specifically expressed in benzene-grown cells. Deletion of one of these, Gmet_3376, inhibited anaerobic benzene oxidation, but not the metabolism of phenol, benzoate, or toluene. The availability of a genetically tractable pure culture that can anaerobically convert benzene to phenol with oxygen derived from water should significantly accelerate elucidation of the mechanisms by which benzene can be activated in the absence of molecular oxygen. Total RNA from three separate cultures of G. metallireducens grown with 250 ÂµM benzene three separate cultures of G. metallireducens grown with 500 ÂµM phenol three separate cultures of G. metallireducens grown with 1 mM benzoate three separate cultures of G. metallireducens grown with 500 ÂµM toluene three separate cultures of G. metallireducens grown with 10 mM acetate were used to study [1] Anaerobic oxidation of benzene by G. metallireducens (Benzene vs. acetate, Benzene vs. benzoate, Benzene vs. phenol, Benzene vs. toluene) [2] Anaerobic oxidation of benzoate by G. metallireducens (Benzoate vs. acetate) [3] Anaerobic oxidation of phenol by G. metallireducens (Phenol vs. acetate) [4] Anaerobic oxidation of toluene by G. metallireducens (Toluene vs. acetate) Each chip measures the expression level of 3,627 genes from G. metallireducens DSM 7210 with nine 45-60-mer probe pairs (PM/MM) per gene, with three-fold technical redundancy.

Dataset Information

(Diacetoxyiodo)benzene-Mediated C-H Oxidation of Benzylic Acetals.

Publications

(Diacetoxyiodo)benzene-Mediated C-H Oxidation of Benzylic Acetals.

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