Rhodium catalyzed [4 + 2 + 2] cycloaddition and alkyne insertion: a new route to eight-membered rings.

A novel variation of the rhodium catalyzed [4 + 2] reaction is reported. A catalyst system that forms an eight-membered ring product from the incorporation of an alkyne into a dienyne is discussed. The products are formed with high diastereoselectivity and in good yield. The highest yields are obtained with alkynes that possess either an oxygen or nitrogen in the propargyl position. Examples are presented where the tether between the alkyne and the diene contains three or four atoms.