Cage-confined catalysis enables asymmetric intermolecular photocycloaddition of (benzo)furans and excited alkenes

Light-driven chemistry has opened a powerful route to molecules that are difficult to build by conventional methods, but one major challenge has remained largely unresolved: how to selectively and asymmetrically dearomatize a non-photoactive aromatic compound while a different molecule absorbs the light. Researchers at Sun Yat-sen University in China have now reported a strategy that addresses this problem using chiral metal–organic cages, creating complex three-dimensional molecules with exceptional control over their structure and handedness.

The study, led by Professors Cheng-Yong Su and Peng Hu, demonstrates the intermolecular asymmetric dearomative photocycloaddition of (benzo)furans with photoactive alkenes. The work, published in the Chinese Journal of Catalysis, uses enzyme-mimetic Δ/Λ-MOC-16 catalysts to organize the reaction inside a confined molecular environment. The resulting process converts relatively flat aromatic starting materials into structurally intricate fused polycyclic products, reaching yields of up to 98 percent, diastereomeric ratios above 20:1, and enantiomeric excesses as high as 99 percent.

Dearomatization is a valuable strategy in synthetic chemistry because aromatic rings are stable, planar, and abundant, while many biologically active molecules contain saturated or partially saturated three-dimensional ring systems. Transforming an aromatic structure into a non-aromatic one can therefore rapidly increase molecular complexity. Photocycloaddition reactions are particularly attractive for this purpose because visible light can activate substrates under relatively mild conditions and generate multiple chemical bonds in a single step.

Most previous photocatalytic dearomatization reactions have relied on excited aromatic compounds reacting with ordinary, ground-state alkenes. In the new approach, the roles are reversed. The (benzo)furan remains in its ground state and acts as the non-photoactive aromatic partner, while the alkene absorbs energy and enters an excited state. This arrangement is chemically demanding because excited alkenes are highly reactive and often short-lived, making it difficult to guide them toward a single reaction pathway or control the formation of one enantiomer over the other.

The researchers addressed this challenge by placing both reaction partners inside a chiral metal–organic cage. These cages are assembled from metal centers and organic ligands to produce hollow molecular architectures with internal cavities. The Δ and Λ forms of MOC-16 create mirror-image confined environments, analogous in some respects to the active sites of enzymes. Within the cage, the substrates are not free to collide randomly in solution. Instead, they can be selectively encapsulated, positioned near one another, and held in an orientation favorable for the desired photocycloaddition.

A combination of mechanistic experiments supported this interpretation. Stern–Volmer quenching studies indicated how the catalyst and substrates interact during the photochemical process, while ultraviolet–visible absorption measurements helped clarify the participation of the photoactive alkene. Control experiments confirmed that the cage was not simply an inert container but played an active catalytic role. Proton nuclear magnetic resonance titration and solubilization studies further showed that the catalyst can dynamically bind the substrates, increasing their effective local concentration and influencing their relative arrangement.

This confined environment is crucial because photocatalytic reactions often suffer from competing pathways caused by the rapid diffusion and high reactivity of excited molecules. The cage restricts the movement and geometry of the excited alkene, while its chiral interior differentiates between the two possible facial approaches to the furan substrate. As a result, the catalyst can simultaneously influence regioselectivity, diastereoselectivity, and enantioselectivity. In practical terms, it helps determine where the new bonds form, how the newly created rings are connected in space, and which mirror-image product predominates.

The reaction also displayed broad substrate tolerance. Cinnamate-derived alkenes and a range of (benzo)furans bearing electronically different substituents were compatible with the method. Substituents at varied positions and groups imposing different degrees of steric hindrance could be accommodated without destroying the selectivity of the transformation. This flexibility is important for medicinal chemistry and materials research, where the ability to modify molecular structures without redesigning an entire synthetic route can greatly accelerate the discovery of useful compounds.

The value of the products extends beyond the initial photocycloaddition. The researchers successfully subjected the cycloadducts to several subsequent transformations, including epimerization, ring-opening reactions, and Suzuki–Miyaura cross-coupling. These reactions demonstrate that the newly generated polycyclic frameworks can serve as versatile intermediates rather than chemically static end products. By combining light activation, asymmetric catalysis, and cage-based molecular recognition, the study establishes a new reaction platform for building complex chiral molecules from comparatively simple starting materials.

The findings highlight the growing potential of metal–organic cages as catalysts that imitate key features of enzymes, including substrate recognition, selective binding, and control within a confined reaction site. They also expand the scope of asymmetric photocatalysis by showing that a ground-state aromatic compound can participate selectively with an excited alkene under the direction of a chiral molecular container. The researchers’ strategy could inspire further cage-catalyzed photochemical reactions and may ultimately contribute to more efficient methods for producing structurally complex molecules relevant to pharmaceuticals, natural-product synthesis, and advanced chemical technologies.

News Publication Date: 11-Jun-2026

Web References: Chinese Journal of Catalysis article page; DOI: 10.1016/S1872-2067(26)65001-2

References: Chinese Journal of Catalysis, “Intermolecular asymmetric dearomative photocycloaddition of (benzo)furans with excited alkenes via cage-confined catalysis.”

Keywords

Photocatalysis, asymmetric synthesis, dearomatization, photocycloaddition, metal–organic cages, enzyme-mimetic catalysis, chiral catalysis, (benzo)furans, excited alkenes, synthetic chemistry