The Release of Singlet Oxygen in the Reaction of Dioxiranes with AmineN-Oxides

Abstract

The reactivity of dimethyldioxirane and methyl(trifluoromethyl)dioxirane towards the amine N-oxides 1a–13a and ammonium derivatives 13b–d has been investigated. In the dioxirane oxidation of the tertiary amines and nitrogen heteroarenes, the expected N-oxides are not always formed. Instead, the in situ generated N-oxides are deoxygenated by the dioxirane with the release of singlet oxygen (1O2) at comparable or even higher rates than the amine oxidation. The amount of 1O2 has been quantified by IR chemiluminescence and by chemical trapping with 9,10-dimethylanthracene. The nucleophilicity of the N-oxide determines the efficacy of the 1O2 release in the deoxygenation. Thus, for the less nucleophilic heteroaromatic N-oxides, the deoxygenation of the amine oxide competes ineffectively with the oxidation of the amine. The ammonium derivatives 13b–d do not promote the decomposition of the dioxiranes; as expected, they are epoxidized.