Electrochemically driven cross-electrophile coupling of alkyl halides

Recent research in medicinal chemistry has suggested that there is a correlation between an increase in the fraction of sp3 carbons—those bonded to four other atoms—in drug candidates and their improved success rate in clinical trials1. As such, the development of robust and selective methods for the construction of carbon(sp3)–carbon(sp3) bonds remains a critical problem in modern organic chemistry2. Owing to the broad availability of alkyl halides, their direct cross-coupling—commonly known as cross-electrophile coupling—provides a promising route towards this objective3–5. Such transformations circumvent the preparation of carbon nucleophiles used in traditional cross-coupling reactions, as well as stability and functional-group-tolerance issues that are usually associated with these reagents. However, achieving high selectivity in carbon(sp3)–carbon(sp3) cross-electrophile coupling remains a largely unmet challenge. Here we use electrochemistry to achieve the differential activation of alkyl halides by exploiting their disparate electronic and steric properties. Specifically, the selective cathodic reduction of a more substituted alkyl halide gives rise to a carbanion, which undergoes preferential coupling with a less substituted alkyl halide via bimolecular nucleophilic substitution to forge a new carbon–carbon bond. This protocol enables efficient cross-electrophile coupling of a variety of functionalized and unactivated alkyl electrophiles in the absence of a transition metal catalyst, and shows improved chemoselectivity compared with existing methods.