Researchers at Ritsumeikan University and Doshisha Women’s College of Liberal Arts published a study on July 26, 2026, detailing a halogen-guided cut-to-fuse
strategy. This method uses chlorine to enable mild, transition-metal-free carbonyl deletion in hydroxycoumarins at room temperature, transforming them into valuable coumaranone scaffolds.
Restructuring a molecule without rebuilding it from scratch remains an essential goal in modern organic chemistry. Skeletal editing helps chemists explore novel chemical structures and simplify the synthesis of compounds with potential pharmaceutical applications. However, for functional groups such as esters, skeletal editing poses a persistent challenge because their carbon–carbon and carbon–oxygen bonds resist cleavage under mild conditions. A research team has introduced a chemistry-based solution inspired by natural product biosynthesis to tackle this hurdle.
Ritsumeikan and Doshisha Researchers Pioneer Halogen Guidance
The research effort was led by Professor Toshifumi Dohi and Yusuke Yoto of Ritsumeikan University, alongside Dr. Hideyasu China of Doshisha Women’s College of Liberal Arts. Their findings were made available online in the journal JACS Au on July 26, 2026. The team demonstrated that introducing chlorine into hydroxycoumarins triggers a precise sequence of bond-cleavage and bond-forming events, removing a carbonyl unit and reconstructing the molecule into a coumaranone framework.
The concept originated from an investigation into a cut-to-fuse
strategy. In this approach, halogenation cuts bonds in a cyclic compound to generate a reactive chain, followed by an intramolecular reaction that fuses the chain into a new heterocyclic structure. The team projected this pathway could achieve carbonyl deletion—the net removal of a carbonyl unit from hydroxycoumarins.
Chlorine Shifts the Reaction Pathway
Initial experiments yielded an unexpected divergence. While investigating fluorine-induced carbon–carbon bond cleavage, fluorination caused the hydroxycoumarin substrate to fragment into separate products instead of reorganizing.
Treating a hydroxycoumarin with N-chlorosuccinimide (NCS) formed a chlorinated intermediate. This intermediate underwent decarbonylative reconstruction, producing a coumaranone rather than causing molecular fragmentation. When the chlorinating reagent was omitted during control experiments, the starting material was recovered unchanged, confirming the necessity of selective chlorination.
Stepwise experiments indicated that chlorination occurs first, followed by decarboxylation and intramolecular cyclization. Optimization of the reaction revealed that the transformation can proceed at room temperature in near-neutral conditions without requiring transition-metal catalysis.
Yields, Substrate Scope, and Practical Scalability
Under optimized conditions involving hydroxycoumarin treated with NCS, water, and sodium acetate in ethyl acetate, followed by potassium phosphate, the reaction produced the model coumaranone in greater than 99% yield. According to the researchers, this represents the mildest nonenzymatic conditions reported to date for the simultaneous cleavage of C–C and C–O bonds involved in this category of carbonyl deletion.
The method demonstrated broad functional group tolerance. Hydroxycoumarins containing methoxy groups, halogens, azides, phenols, carboxylic acids, and boron-containing functionalities were accommodated successfully. Substrates bearing substituted aromatic rings, naphthalene, pyridine, thiophene, furan, and aliphatic groups also produced good to excellent yields, and a related cyclic beta-keto ester underwent reconstruction to prove the chemistry is not restricted to a single class.
On a gram scale, the model reaction delivered the desired coumaranone in 91% yield. This resulting scaffold allows for downstream functionalization, including conversion to a benzofuran, introduction of a quaternary carbon center, and transition-metal-catalyzed coupling reactions.
Future Implications for Medicinal Chemistry
By bypassing the harsh conditions traditionally required for ester bond cleavage, the halogen-guided approach offers a streamlined pathway for generating structural diversity in drug discovery. A coumaranone bearing a boron pinacol ester proved directly applicable for palladium-catalyzed coupling without requiring isolation, pointing to immediate utility for downstream synthesis.
The research is documented under the original paper title Halogen-Guided Reconstructive Transformation of Hydroxycoumarin to Coumaranone
in the journal JACS Au, providing chemists with a transition-metal-free alternative for skeletal editing.
