Palladium-catalyzed [3+2] intramolecular cycloaddition of alk-5-ynylidenecyclopropanes: a rapid, practical approach to bicyclo[3.3.0]octenes.

Readily accessible hex-5-ynylidenecyclopropane derivatives cycloisomerize to bicyclic five-membered carbocycles upon heating with catalytic amounts of a palladium complex.