Premium
Boosting Molecular Complexity with O 2 : Iron‐Catalysed Oxygenation of 1‐Arylisochromans through Dehydrogenation, Csp 3 −O Bond Cleavage and Hydrogenolysis
Author(s) -
GonzalezdeCastro Angela,
Robertson Craig M.,
Xiao Jianliang
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201806117
Subject(s) - dehydrogenation , hydrogenolysis , bond cleavage , cleavage (geology) , chemistry , oxygenation , catalysis , stereochemistry , materials science , organic chemistry , medicine , anesthesia , fracture (geology) , composite material
Oxidative cleavage of the Csp 3 −O bond in 1‐arylisochromans with stoichiometric oxidants, such as CrO 3 /H 2 SO 4 , has been practiced for decades in synthetic chemistry. Herein, we report that a structurally well‐defined Fe II –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 3 −O bond cleavage at the iron centre and hydrogenolysis of the resulting Fe−O bond with the H 2 generated from the dehydrogenation step. In the absence of H 2 but under iron catalysis, the peroxide intermediate is converted into an unexpected ketal compound, which transfers into a 2‐(hydroxyethyl)benzophenone when both O 2 and H 2 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.