Divergent Transformations of Cobaltacyclobutenes Generated from [2 + 2]-Cycloadditions of Vinylidenes and Alkynes.

A cobalt-catalyzed addition of a vinylidene equivalent to an alkyne generates a cobaltacyclobutene intermediate. In the presence of Zn(OTf)2, the metallacycle undergoes a Co-to-Zn transmetallation process to form an organozinc species, amenable to quenching with water or other electrophiles to yield trans-1,3-dienoid products. Alternatively, interception of the metallacycle by other π-systems under modified conditions furnishes cyclic polyene products. This dual platform enables the synthesis of diverse molecular scaffolds from a single intermediate and highlights the versatility of metallacycles generated by vinylidene transfer reactions.