Iron-Mediated Electrochemical Cyclopropanation of Borodiiodomethane with Alkenes

Abstract

Cyclopropane is a unique ring motif widely incorporated into pharmaceuticals to enhance their potency. Developing synthetic methods for the efficient construction of cyclopropanes, particularly those with functional groups, is of both practical significance and academic interest. Among the reported methods, the reduction of gem-dihalides followed by cyclization with alkenes represents one of the most efficient and straightforward [2+1] approaches. However, most references rely on photochemical pathways, which severely limit practical applications. Additionally, electrochemical catalytic reduction of halides has gained significant attention in recent years, primarily using nickel and cobalt catalysts. In this study, we introduce an iron-mediated electrochemical reduction of borodiiodomethane, followed by cyclopropanation with alkenes, enabling rapid fabrication of cyclopropylboronates. Substrates with a wide range of functional groups are well tolerated, demonstrating the ease of late-stage modifications. Gram-scale synthesis, conducted without extending reaction time and maintaining the same current density, yielded similar results, highlighting the method's practical application. The boronate group on the cyclopropane can be easily transformed, paving the way for further applications in medicinal chemistry. Notably, mechanistic investigations, including control experiments and cyclic voltammetry studies, revealed that iron species—both the Fe salt and the Fe/2,2'-biquinoline complex—can effectively promote electrochemical cyclopropanation. Given that iron is an inexpensive material, its dual role as both sacrificial anode and promoter enhances the practicality of this method.

Keywords

Iron-mediated / Electrochemical reduction / Cyclopropane / Cyclopropylboronate / [2+1] / Medicinal chemistry / gem-Dihalide / Late-stage modification

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