For over a century and a half, chemists have principally relied on elimination reactions, first detailed in the 1860s, to forge carbon-carbon triple bonds from double bonds. These classical procedures typically involve strong bases or necessitate elevated temperatures, conditions that can jeopardize the integrity of sensitive functional groups. Such stringent requirements circumscribe the method’s application to relatively simple molecules and impede its use in late-stage functionalization of complex, biologically relevant substrates. Consequently, the direct transformation of alkenes to alkynes has remained a formidable synthetic challenge.

Breaking through these longstanding limitations, a novel frontier has emerged from recent research led by Meng, Liang, Xu, and their colleagues, who have pioneered a groundbreaking method that transcends traditional elimination chemistry. This transformative approach capitalizes on a recyclable selenanthrene reagent, crafted to drive the desaturation of alkenes into alkynes under remarkably mild reaction conditions. The innovation is not merely a tweak of existing methodologies but a quantum leap forward, enhancing the accessibility of alkynes while preserving delicate molecular architectures.

At the core of this new chemistry lies the subtle yet powerful utility of selenanthrene, a selenium-containing heterocycle whose unique reactivity profile facilitates the removal of hydrogen atoms from alkenic substrates. The reagent operates in a manner that circumvents the reliance on strongly basic environments or elevated thermal input. This breakthrough ensures that a broader spectrum of functional groups—often incompatible with the harsh elimination protocols—can now be accommodated. As a result, the reaction expands its reach into spaces previously deemed challenging or outright inaccessible.

The synthetic elegance of this transformation amplifies its practical significance. The selenanthrene reagent is not consumed irreversibly but instead is designed for recyclability, fostering sustainability and reducing waste. This recyclability contrasts sharply with many stoichiometric reagents used in organic synthesis, which generate significant byproducts. Multiplying its value, the method displays broad substrate scope compatibility, adeptly handling traditional leaving groups alongside sensitive moieties that benefit from the gentle reaction environment.

Beyond mere desaturation, the innovation’s implications permeate the subtleties of molecular stereochemistry. The method enables not only the efficient generation of alkynes but also the inversion or “sorting” of alkene (Z/E) isomer configurations. Such stereochemical manipulations were previously difficult to achieve with routine protocols. This advancement holds profound implications for downstream derivatization strategies, as the geometric relationship between substituents on double bonds profoundly influences the reactivity and interaction of molecules in synthetic and biological contexts.

The capacity to invert (Z/E) configurations with ease expands synthetic flexibility. It empowers chemists to selectively access specific alkene isomers that serve as crucial intermediates or final targets in pharmaceutical and material science applications. Traditional methods often fail to differentiate isomers cleanly or require multiple steps with associated loss of yield and selectivity. The selenanthrene-mediated platform offers a streamlined solution, potentially revolutionizing how stereochemical challenges are approached.

Importantly, this method thrives in late-stage functionalization scenarios, where molecular complexity and functional group diversity are at their peak. This utility catalyzes a paradigm shift in synthetic strategy, enabling chemists to introduce alkynes—or reintroduce them at advanced synthetic junctions—without compromising the integrity of other sensitive functionalities. Such finesse enhances the efficiency and reduces the total number of synthetic steps, which is invaluable in the synthesis of natural products, pharmaceuticals, and advanced materials.

From a mechanistic perspective, the interplay between the selenanthrene reagent and the alkene substrate likely involves an orchestrated sequence of redox and elimination steps that delicately tune the reaction pathway. Although full mechanistic details await further elucidation, this process exemplifies how mechanistic insight drives the design of tailored reagents that marry reactivity with selectivity. It underscores the evolving sophistication within synthetic organic chemistry, where traditional transformations are reimagined with molecular precision.

The broader implications of this discovery resonate across diverse fields. In medicinal chemistry, the method could enhance the late-stage diversification of drug candidates, expediting the exploration of chemical space and improving molecule design cycles. In material sciences, the facile preparation of alkynes with complex functionalities could streamline the synthesis of conjugated materials, polymers, and nanostructures. The eco-friendly aspect of reagent recyclability aligns with the burgeoning emphasis on green chemistry principles.

This breakthrough arrives at a pivotal moment, addressing a synthetic bottleneck that has persisted despite alkynes’ central role. By enabling milder, more selective conversion of alkenes to alkynes, the research charts a new course for organic synthesis, harmonizing practicality with innovation. It invites a reexamination of longstanding synthetic paradigms and fuels excitement for future discoveries built on this foundation.

As research advances, further investigations into reaction scope nuances, mechanistic probes, and the development of even more efficient or catalytic variants may expand the method’s impact. Collaborative efforts integrating computational modeling, mechanistic studies, and applied chemistry will likely accelerate the translation of this technology into widespread laboratory and industrial settings.

In sum, this elegant and pragmatic approach represents a milestone in synthetic organic chemistry. The recyclable selenanthrene reagent-mediated desaturation of alkenes to alkynes under mild conditions opens doors that have long stood closed. Its capacity for broad functional group compatibility, stereochemical control, and sustainable operation heralds a new era in the construction and modification of carbon-carbon multiple bonds.

Subject of Research: Organic synthetic methodology; selective alkene to alkyne conversion using a recyclable selenanthrene reagent

Article Title: Direct conversion from alkenes to alkynes

Article References:
Meng, J., Liang, Y., Xu, R. et al. Direct conversion from alkenes to alkynes. Nature (2026). https://doi.org/10.1038/s41586-026-10372-3

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Despite its potential, asymmetric catalysis via MHAT has remained a formidable challenge. Central to this difficulty is the inherently weak interaction between transient prochiral organic radicals and chiral catalysts. Radical species are often fleeting and poorly controlled, complicating efforts to induce enantioselectivity—control over the spatial arrangement of atoms that defines a molecule’s three-dimensional shape and its biological activity. Overcoming these limitations is pivotal, as asymmetric radical processes can unlock pathways to enantioenriched products highly valued in pharmaceuticals and agrochemicals.

Addressing this gap, a recent breakthrough harnesses the versatility of cytochrome P450 enzymes (CYPs)—nature’s own catalysts known for their versatile oxidative transformations. Recognized chiefly for their ability to activate molecular oxygen and perform selective oxidations, certain CYPs have now been repurposed to catalyze MHAT, a reaction that does not naturally occur in biological systems. This pioneering endeavor employed directed evolution, a technique that mimics natural selection in the laboratory to iteratively improve enzyme performance. Starting with a variant of the P450_BM3 enzyme, researchers developed a triple mutant capable of performing radical cyclizations on unactivated alkenes with remarkable stereocontrol.

The evolved P450_BM3 mutant demonstrated the ability to catalyze MHAT radical cyclization reactions that forge diverse cyclic amines such as pyrrolidines and piperidines—structural motifs frequently encountered in bioactive molecules. These transformations were achieved under aerobic whole-cell conditions, highlighting the practicality and robustness of the biocatalytic system. Strikingly, the reactions produced enantiomeric ratios as high as 98:2, signifying exceptional control over the stereochemical outcome and marking a notable advance in asymmetric radical chemistry.

Beyond substrates with electron-deficient alkenes, the repurposed enzymes expanded their substrate scope to include alternative radical acceptors such as hydrazones, oximes, and nitriles. This breadth underscores the enzyme’s adaptability and the potential for broad application in synthesizing structurally diverse heterocycles. The integration of these unconventional radical acceptors suggests new strategic avenues for assembling complex architectures in synthetic chemistry, combining the power of enzymatic precision with radical reactivity.

Mechanistic investigations into the catalytic cycle revealed that the enzyme operates through an MHAT pathway initiated by homolytic cleavage of a transient iron(III)–hydride intermediate. This fleeting species is central to the reaction, mediating hydrogen atom transfer to initiate radical formation. The homolytic cleavage contrasts with the more common heterolytic mechanisms of metal–hydride species and opens new mechanistic spaces that enzymes can exploit. These mechanistic insights also provide a blueprint for further engineering of enzymes tailored for radical transformations, guided by understanding how metalloenzymes can harness homolytic metal–hydride chemistry.

A testament to the power of directed evolution, starting from a different cytochrome P450 scaffold—CYP119—researchers evolved a stereocomplementary MHATase that delivers the opposite enantiomeric product with equally high selectivity. This stereocomplementarity showcases the tunability of enzymatic systems through iterative mutation and selection, enabling fine control over stereochemical outcomes and expanding practical synthetic capabilities. The availability of two complementary enzymes offers synthetic chemists versatile tools for stereodivergent synthesis, an essential aspect of drug discovery and development.

This groundbreaking work exemplifies how the natural versatility of metalloenzymes can be expanded by engineering novel reactivities, extending beyond their canonical functionalities. By integrating homolytic metal–hydride reactivity into biocatalysts, this study charts a course toward a new class of asymmetric radical biocatalysts. Such catalysts could revolutionize synthetic strategies by marrying the selectivity and sustainability of enzymatic approaches with the expansive reaction space accessible via radical intermediates.

The implications of this discovery extend beyond academic curiosity. Enzymatic MHAT catalysis has the potential to transform synthetic routes to chiral nitrogen heterocycles, privileged motifs in medicinal chemistry. The mild reaction conditions, use of whole-cell catalysts, and high stereoselectivity promise greener, more efficient synthetic processes that could supplant harsher traditional methods relying on metal complexes or radical initiators. Moreover, the ability to perform late-stage functionalizations on complex molecules opens doors to rapid diversification of pharmaceuticals and natural products.

Future avenues of research include expanding substrate scope to even more challenging alkenes and radical acceptors, optimizing enzyme stability and turnover in industrial settings, and combining MHAT biocatalysis with other enzymatic or chemical transformations in cascade sequences. Such integrated approaches could enable streamlined syntheses of molecules with dense stereochemical information, tackling synthetic challenges that have long stymied chemists.

Overall, this landmark study underscores a paradigm shift in asymmetric catalysis, where the power of radical intermediates traditionally constrained by lack of selectivity is now harnessed with exquisite control via engineered enzymes. It demonstrates the promise of melding bioinspiration with chemical innovation to unlock new frontiers in molecular synthesis.

As the toolkit of biocatalysis expands with innovative MHATases, synthetic chemists stand at the cusp of a radical revolution—one where enzymes not only mimic but also transcend natural capabilities to access previously elusive chemical space. In this dynamic interplay of radical chemistry and enzyme engineering, the future of asymmetric synthesis gleams brightly.

Subject of Research: Repurposing cytochrome P450 enzymes to catalyze asymmetric metal-hydride hydrogen atom transfer (MHAT) for radical hydrofunctionalization of unactivated alkenes.

Article Title: Repurposing haemoproteins for asymmetric metal-catalysed H atom transfer.

Article References:
Zhang, X., Chen, D., Álvarez, M. et al. Repurposing haemoproteins for asymmetric metal-catalysed H atom transfer. Nature (2025). https://doi.org/10.1038/s41586-025-09308-0

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