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Title: Photoinduced Reactivity in a Dispiro-1,2,4-trioxolane: Adamantane Ring Expansion and First Direct Observation of the Long-Lived Triplet Diradical Intermediates
Authors: Brás, Elisa M
Cabral, Lília I L
Amado, Patrícia S M
Abe, Manabu
Rui Fausto 
Cristiano, Maria L S
Keywords: Photodissociation; Infrared light; Electron paramagnetic resonance spectroscopy; Quantum mechanics; Irradiation
Issue Date: 28-May-2020
Publisher: ACS Publications
Project: info:eu-repo/grantAgreement/FCT/UID/QUI/0313/2019/PT 
Serial title, monograph or event: The Journal of Physical Chemistry. A
Volume: 21
Issue: 124
Abstract: Dispiro-1,2,4-trioxolane, 1, an ozonide with efficient and broad antiparasitic activity, was synthesized and investigated using matrix isolation FTIR and EPR spectroscopies together with both B3LYP/6-311++G(3df,3dp) and M06-2X/6-311++G(3df,3dp) theoretical methods. Irradiations (λ ≥ 290 nm) of the matrix isolated 1 (Ar or N2) afforded exclusively 4-oxahomoadamantan-5-one, 4, and 1,4-cyclohexanedione, 5. These results suggested that the reaction proceeded via a dioxygen-centered diradical intermediate, formed upon homolytic cleavage of the labile peroxide bond, which regioselectively isomerized to form the more stable (secondary carbon-centered)/oxygen-centered diradical. In situ EPR measurements during the photolysis of 1 deposited in a MeTHF-matrix led to the detection of signals corresponding to two triplet species, one of which was short-lived while the other proved to be persistent at 10 K. These observations strongly support the proposed mechanism for the photogeneration of 4 and 5, which involves intramolecular rearrangement of the intermediate diradical species 2 to afford the triplet diradical 3.
ISSN: 1089-5639
DOI: 10.1021/acs.jpca.0c01974
Rights: embargoedAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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