Cyclobutenes are not necessary intermediates in the skeletal rearrangement of enynes, which is supported DFT calculations and kinetic studies. Cyclobutenes may arise from the corresponding syn-cyclopropyl gold(I) carbenes.
Divergent Mechanisms for the Skeletal Rearrangement and [2+2] Cycloaddition of Enynes Catalyzed by Gold
Angew. Chem. Int. Ed. 2005, 44, 6146-6148.