Boosting Molecular Complexity with O<sub>2</sub>: Iron-Catalysed Oxygenation of 1-Arylisochromans through Dehydrogenation, Csp<SUP>3</SUP>-O Bond Cleavage and Hydrogenolysis



Gonzalez-de-Castro, Angela, Robertson, Craig M ORCID: 0000-0002-4789-7607 and Xiao, Jianliang ORCID: 0000-0003-2010-247X
(2019) Boosting Molecular Complexity with O<sub>2</sub>: Iron-Catalysed Oxygenation of 1-Arylisochromans through Dehydrogenation, Csp<SUP>3</SUP>-O Bond Cleavage and Hydrogenolysis. CHEMISTRY-A EUROPEAN JOURNAL, 25 (17). pp. 4345-4357.

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Abstract

Oxidative cleavage of the Csp<sup>3</sup> -O bond in 1-arylisochromans with stoichiometric oxidants, such as CrO<sub>3</sub> /H<sub>2</sub> SO<sub>4</sub> , has been practiced for decades in synthetic chemistry. Herein, we report that a structurally well-defined Fe<sup>II</sup> -pyridyl(bis-imidazolidine) catalyst promotes the aerobic oxygenation of 1-arylisochromans, affording highly selectively 2-(hydroxyethyl)benzophenones, compounds of potential for neuroprotective agents. Key intermediates have been isolated, indicating that the reaction proceeds through dehydrogenative oxygenation of the isochromans at the 1-position, Csp<sup>3</sup> -O bond cleavage at the iron centre and hydrogenolysis of the resulting Fe-O bond with the H<sub>2</sub> generated from the dehydrogenation step. In the absence of H<sub>2</sub> but under iron catalysis, the peroxide intermediate is converted into an unexpected ketal compound, which transfers into a 2-(hydroxyethyl)benzophenone when both O<sub>2</sub> and H<sub>2</sub> are admitted. The unique ability of the iron catalyst for oxygenation and hydrogenation in the same catalytic process under mild conditions allows for the stepwise preparation of a variety of isolable oxygenated products on a preparative scale, circumventing the need for using wasteful and/or toxic oxidants.

Item Type: Article
Uncontrolled Keywords: autoxidation, dioxygen, iron, isochromans, oxidation
Depositing User: Symplectic Admin
Date Deposited: 21 Mar 2019 11:36
Last Modified: 07 Feb 2024 21:31
DOI: 10.1002/chem.201806117
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3034588