Rhodium-catalyzed synthesis of eight-membered rings.

Experiments to develop a rhodium catalyst for the [4 + 2 + 2] cycloisomerization of dienynes with a second alkyne are described. The generality of the reaction is probed in terms of dienyne structure and alkyne structure. A catalyst system that provides cyclooctatrienes in greater than 70% yield is reported. Several experiments to determine the nature of the catalyst are described.