Electrochemical Aerobic Oxidation of Aminocyclopropanes to Endoperoxides

摘要

The oxidation of cyclopropanes to 1,2-dioxolanes has been documented for almost 40 years and has been performed on many substrates under various conditions. Among these, very few examples involve aminocyclopropanes. The transformation of secondary cyclopropylamines into alpha-amino endoperoxides by autocatalytic aerobic oxidation was reported by Wimalasena et al. a few years ago. It was found that a catalytic amount of tris(1,10-phenantroline)iron-(III) hexafluorophosphate, or hydrogen-abstracting agents such as benzoyl peroxide or tert-butyl peroxide under UV irradiation, could increase the reaction rate. A similar transformation was observed in our laboratory, spontaneously occurring in the presence of air and silica gel from electron-rich tertiary arylcyclopropylamines. In this case, as well as in the iron-catalyzed process, the mechanism probably involves a one-electron oxidation of the substrate to a cation radical intermediate. After cyclopropane ring opening, reaction with oxygen, and ring closure, the newly produced cation radical would be able to function as an oxidant itself and thus close the catalytic cycle (Scheme 1).