Formation of six-membered rings via alkyne insertion into four-membered rings

Alkyne insertion into four-membered carbocyclic rings was achieved through rhodium(I)-catalyzed C–C bond cleavage. The reaction of (2-pyridylmethylene)cyclobutenes proceeded via C–C oxidative addition, and that of cyclobutenols involved β-carbon elimination. In both the cases, multiply substituted benzenes were obtained through the aromatization of the initially formed 1,4-cyclohexadienes.