Synthesis and oxygen-atom transfer reactions of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes

A series of 3-hydroperoxy-3,4,4,5,5-pentasubstituted-1,2-dioxolanes 2a-d were synthesized in good yield from the corresponding 3-hydroxy-1,2-dioxolanes by reaction with concentrated hydrogen peroxide in acetonitrile with p-toluenesulfonic acid as catalyst. The 3-hydroperoxy-1,2-dioxolanes were effective oxygen-atom transfer reagents for the oxidation of thioanisole, triethylamine and 2,3-dimethyl-2-butene to the sulfoxide, N-oxide and epoxide, respectively. The reactions occurred under mild conditions and were found to be of the second order overall. The second order late constants (k(2)) were determined for oxidation of thioanisole by 2a-d in deuteriochloroform. For 2a, k(2) values for N-oxidation and epoxidation were also measured. The 3-hydroperoxy-1,2-dioxolanes were found to be less reactive than the structurally similar cyclic alpha-azohydroperoxides but much more reactive than simple hydroperoxides. The mechanism of oxygen-atom transfer is postulated to occur via nucleophilic attack of the substrate on the terminal oxygen of the hydroperoxide. Intramolecular hydrogen bonding of the hydroperoxy proton to a dioxolane oxygen appears to account for the reaction order in aprotic media.