Oxidative free-radical additions of α-nitro ketones and α-nitro amides to alkenes and alkynes mediated by electrochemically regenerable manganese(III) acetate

Abstract

Manganese(III) acetate mediated oxidative additions of the α-aryl α-nitro ketones 1 and 9 to simple alkenes forms the isoxazoline N-oxides 3 and 10 as the main products in 13–62% yield. Depending upon the structure of the unsaturated system used, the α-allylated α-nitro ketones 4, the tricyclic product 5 or the aromatised isoxazole 7 were also obtained. The oxidative addition of α-methyl α-nitro ketones 11 to hex-1-ene has been shown to yield the γ-acetoxylated α-nitro ketones 12. Based upon the influence of substituents in both the α-nitro ketone and the alkene, the outcome of the reaction mechanism is discussed. The oxidative addition of α-nitro amides 13 to hex-1-ene furnished the cyclic nitronates 14 together with the isoxazolines 15, which have been shown to be formed independently during the course of the reaction. Representative oxidative radical additions were performed using anodically in situ generated manganese(III) acetate from catalytical amounts of manganese(II) acetate. In these cases, yields as high, or even slightly higher, were obtained compared to those reactions employing 2 molar equiv. of the transition metal oxidant.