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.