Mechanochemical Murai C–C Bond Activation: Solventless, Ligand-Free Decarbonylative Coupling of Indole Esters

The ruthenium-catalyzed Murai reaction represents a fundamental C–H activation process wherein the nucleophilic ruthenium(0) catalyst oxidatively inserts into inert C–H bonds, which has been broadly utilized in all areas of chemical science. Herein, we report the first ruthenium-catalyzed decarbonylative cross-coupling of indole carboxylic acid esters via Murai carbon–carbon bond cleavage under solventless mechanochemical conditions. A key feature of this reaction involves mechanochemical carbon–carbon bond activation, a process that has been elusive despite a very significant progress in mechanochemical C–H bond activation. The catalytic system enables the simultaneous activation of ester C–O/C–C bonds through ruthenium catalysis, achieving a highly chemoselective decarbonylative coupling with common arylboronic acids. Notably, the reaction proceeds without added ligands, bases, or organic solvents, establishing a sustainable platform for ruthenium-catalyzed transformations. The mechanistic insights lay the groundwork for the future design of catalytic Murai activation methodologies under solventless mechanochemical conditions. This mechanochemical decarbonylative coupling represents an innovative and green strategy to access structurally diverse indole derivatives─privileged motifs in pharmaceuticals and functional materials.