Carbon-carbon bond formation is the backbone of organic synthesis, and the reactions that accomplish it define what molecules are practically accessible. Bonds between two sp3-hybridised carbons, the tetrahedral carbons that give molecules their three-dimensional shape, are particularly valuable. Saturated, three-dimensional frameworks are strongly associated with success in drug development, a trend famously described as escaping flatland, because flat, aromatic-rich molecules often suffer from poor solubility and off-target effects. Yet while chemists have become adept at stitching together flat sp2 carbons through classic cross-coupling chemistry, the alkyl-alkyl variant remains far more difficult, because the reactive intermediates involved are short-lived and prone to unproductive side reactions.

One powerful way to make sp3-sp3 bonds is radical chemistry. Radicals, species bearing an unpaired electron, are notoriously reactive, which makes them both useful and dangerous in a synthesis flask. When two radicals meet, they can combine to form a new carbon-carbon bond, a process known as radical-radical cross-coupling. The catch is controlling the encounter. Most successful strategies to date rely on pairing a persistent radical, one that survives long enough to accumulate in solution, with a transient radical, one that lives for only a fleeting moment. The persistent radical effect then steers the chemistry toward selective cross-coupling rather than a chaotic mixture of products. Directly coupling two transient radicals, both generated from separate precursors, has remained a formidable challenge.

There is one venerable exception: Kolbe electrolysis, first described by Hermann Kolbe in 1849. In this electrochemical process, carboxylic acids are oxidised at an anode, losing an electron and releasing carbon dioxide to generate carbon-centred radicals that then dimerise. Kolbe electrolysis is one of the few methods capable of directly coupling two transient radicals, but it works best when both radicals come from the same or very similar carboxylic acids. Getting radicals from two chemically distinct precursors, say a carboxylic acid on one side and a boronic acid on the other, to meet and combine selectively has largely been out of reach, because the two precursors oxidise at different potentials and their radicals tend to react with themselves rather than with each other.

The Northwestern team’s solution rests on two intertwined ideas. The first is redox-matched alternating-polarity electrolysis. Instead of applying a constant current in one direction, the researchers alternate the polarity of the electrodes, so that each half-cycle generates one type of radical under conditions matched to its own oxidation chemistry. This waveform control allows carboxylic acids to be oxidised to alkyl radicals during one polarity phase, while organoboron reagents are activated during the complementary phase, giving both radical pools a chance to coexist and combine. Alternating current electrolysis has been gaining momentum in organic electrosynthesis precisely because it lets chemists run incompatible oxidative and reductive events in the same vessel, and the team’s earlier mechanistic work on alternating-polarity electrolysis for carbon-centred radical generation laid the groundwork for the present advance.

The second idea is controlled activation of redox-active species through fluoride. Organoboron reagents are not normally easy to oxidise directly, but the researchers used controlled fluoride activation to tune the redox behaviour of the boronic acids, making them competent radical precursors under the electrolysis conditions. Cyclic voltammetry studies, an electrochemical technique that maps out at which potentials molecules gain or lose electrons, helped the team identify the redox-matched window in which both precursors could be activated without one simply overwhelming the other. By carefully choreographing electrode polarity and chemical activation, the method achieves what conventional constant-current electrolysis cannot: a productive meeting of two transient radicals born from entirely different functional groups.

The scope of the transformation is what makes the result more than an electrochemical curiosity. The researchers demonstrated the cross-coupling of alkyl carboxylic acids with alkyl boronic acids to form sp3-sp3 carbon-carbon bonds, exactly the connectivity that is prized in drug-like scaffolds but difficult to access. They also showed that the platform extends to homocoupling reactions, in which two identical fragments are joined, and to a net carboxylic acid-alkene cross-coupling. In the latter variant, an alkene is first converted in situ into an alkyl boronic acid through hydroboration, the addition of a boron-hydrogen bond across the double bond, and the resulting boronic acid then enters the electrolytic coupling. This effectively lets chemists use cheap, widely available alkenes as radical precursors without isolating the intermediate.

Perhaps most striking is the way the new chemistry dovetails with established catalytic reactions. The team showcased tandem processes in which the electrochemical radical coupling is combined with Suzuki coupling, the palladium-catalysed workhorse reaction that joins boronic acids with aryl halides, and with Buchwald-Hartwig amination, which forms carbon-nitrogen bonds. This means a single molecular sequence can build a carbon-carbon bond electrochemically and then diversify the product through trusted catalytic steps, multiplying the value of each starting material. For medicinal chemists, who routinely need to prepare families of closely related analogues to optimise a drug candidate, such downstream diversification from a common carboxylic acid-boronic acid coupling product is exactly the kind of flexibility that accelerates discovery.

The significance of the work lies in the feedstocks as much as in the chemistry. Carboxylic acids and organoborons are among the most plentiful and well-behaved functional groups in the synthetic repertoire, stable enough to store and handle, and available in enormous structural variety. Electrochemistry itself has undergone a renaissance in the past two decades, because electricity can serve as a clean, tunable oxidant or reductant, replacing stoichiometric chemical oxidants and offering precise control over reaction outcomes through potential and current. By merging waveform-controlled electrolysis with rational redox matching, the Northwestern group has pushed that renaissance into territory that classical methods, including more than a century and a half of Kolbe chemistry, could not reach.

There remain practical considerations before such methods become routine. Alternating-polarity electrolysis requires equipment and optimisation that many synthetic laboratories are still adopting, and the interplay of electrode material, supporting electrolyte, solvent and waveform parameters demands careful tuning for each new substrate combination. The mechanistic picture, probed through cyclic voltammetry and experimental studies of radical generation, will continue to be refined as the community explores the boundaries of the approach. Nevertheless, the demonstration that two transient radicals from distinct, abundant precursors can be generated in the same pot and persuaded to couple selectively marks a genuine expansion of what electroorganic synthesis can do. For a field whose ultimate goal is to make any desired molecule efficiently, sustainably and in three dimensions, the ability to weld carboxylic acids and organoborons together with nothing more than electrons is a milestone worth watching.

Subject of Research: Electrochemical radical-radical cross-coupling of alkyl carboxylic acids and organoboronic acids

Article Title: The radical-radical cross-coupling of alkyl carboxylic acids and organoborons

Article References: Zhong, J., Boudjelel, M., Evans, J. M., Vanswearingen, I., & Malapit, C. A. (2026). The radical-radical cross-coupling of alkyl carboxylic acids and organoborons. Nature Chemistry. https://doi.org/10.1038/s41557-026-02237-z

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02237-z

Keywords: electrochemistry, radical cross-coupling, carboxylic acids, organoborons, Kolbe electrolysis, C(sp3)-C(sp3) bonds, organic synthesis, alternating polarity electrolysis, Nature Chemistry, synthetic methodology, persistent radical effect, medicinal chemistry