Electrochemical Cycloaddition Reactions of Alkene Radical Cations – a Route Towards Cyclopropanes and Cyclobutanes

Abstract

New methods to promote single-electron transfer reactions play an increasingly important role in driving modern organic chemistry. Significant advances have been made in the field of photoredox catalysis1 and synthetic organic electrochemistry2 to expand the utility of radicals in organic synthesis.3 While the initial developments in synthetic organic electrochemistry date as far back as the early 19th century, only recently has it undergone an explosive revival and it is now an important part of synthetic organic chemistry.4 Undeniably, it provides a green alternative to known and new reactive intermediates by the promotion of organic reactions under mild conditions without the necessity for excessive amounts of hazardous and wasteful oxidants and reductants, metals4 or catalysts, making chemical synthesis highly atom economical.5 Our work describes mild and efficient electrochemical methods for [2+1] and [2+2] cycloaddition reactions of alkene radical cations. Anodic oxidation of olefins produces electrophilic alkene radical cations, which further react with nucleophilic diazo compounds in a formal [2+1] cycloaddition towards cyclopropane synthesis. This methodology is also applicable for [2+2] cycloadditions with styrene derivatives, validating this efficient electrochemical system for both cyclopropane and cyclobutane ring synthesis. The advantages of this methods include the mild, metal and catalyst free conditions, simple setup, and scalability of the procedure, as well as its potential use for industrial applications since the method requires non-expensive graphite electrodes.