The SN2 Reactivity of 3,3-Disubstituted 1,2-Dioxetanes with Morpholine

Article abstract of DOI:10.1021/jo00114a044

The reaction of morpholine with the 3-aryl-3-methyldioxetanes 1a-c (Y = 4-OMe, H, 4-NO2), the 3-(methoxymethyl)-3-phenyldioxetane (1d), and the 3-(halomethyl) 3-phenyldioxetanes 1e,f (X = Cl, Br) was investigated to determine the S_N2 reactivity of these dioxetanes and the product distribution of the hydroxylamine ether 2 adducts and the dioxetane fragmentation products 3.It was shown that the overall reactivity and the product distribution are strongly dependent on the substituents of the dioxetanes 1.Thus, the reactivity of the dioxetanes 1 toward morpholine was demonstrated to correlate with the electron-accepting propensity of the substituents in the 3-position, while the product distribution depends on the electronic features of the primary dipolar adduct, which results from nucleophilic attack at the dioxetane peroxide bond.Electron-donating substituents (Y = 4-OMe) favor proton transfer from the hydroxylammonium site to the alkoxide ion due to the enhanced basicity of the latter, and, therefore, the formation of the hydroxylamine ether 2 is promoted.Additionally, electron-accepting substituents (Y = NO2) facilitate the Grob fragmentation of the primary dipolar adduct to the dioxetane cleavage products 3.The unexpected formation of the hydroperoxide 4f in the reaction of the dioxetane 1f with morpholine was shown to result from acid-catalyzed ring opening of the dioxetane by morpholinium bromide and subsequent morpholine trapping of the resulting stabilized, bromine-bridged benzylic cation.