Cycloaddition of Cyclopropenes with Alkynes via Carbon–Carbon Double Bond Cleavage Enabled by a Ruthenium Catalyst: Synthesis of Cyclopentadienes and Cycloheptatrienes

Transition-metal-mediated carbon–carbon single-bond cleavage of cyclopropenes has been widely exploited in organic synthesis. However, the ring-opening of cyclopropenes via the cleavage of their carbon–carbon double bond remains a formidable challenge. Herein, we report an intramolecular cycloaddition of cyclopropenes with alkynes via cleavage of the carbon–carbon double bond of cyclopropenes enabled by a ruthenium catalyst to afford 1,2-fused cyclopentadienes, which are difficult to access by conventional synthetic methods. Density functional theory calculations indicate that the reaction proceeds via a cyclopropane-fused ruthenacycle that undergoes ring expansion to generate a six-membered cyclic biscarbenoid. We also synthesized fused cycloheptatrienes via the cycloaddition of cyclopropene–diynes.