THE S(N)2 REACTIVITY OF 3,3-DISUBSTITUTED 1,2-DIOXETANES WITH MORPHOLINE

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 investigat ed to determine the S(N)2 reactivity of these dioxetanes and the produ ct distribution of the hydroxylamine ether 2 adducts and the dioxetane fragmentation products 3. It was shown that the overall rectivity and the product distribution are strongly dependent on the substituents o f the dioxetanes 1. Thus, the reactivity of the dioxetanes 1 toward mo rpholine was demonstrated to correlate with the electron-accepting pro pensity of the substituents in the 3-position, while the product distr ibution depends on the electronic features of the primary dipolar addu ct, which results from nucleophilic attack at the dioxetane peroxide b ond. 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 hydroxyl amine ether 2 is promoted. Additionally, electron-accepting substituen ts (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 If with morph oline was shown to result from acid-catalyzed ring opening of the diox etane by morpholinium bromide and subsequent morpholine trapping of th e resulting stabilized, bromine-bridged benzylic cation.