Ruthenium-Catalyzed Cycloisomerization of cis-3-En-1-ynes to Cyclopentadiene and Related Derivatives through a 1,5-Sigmatropic Hydrogen Shift of Ruthenium−Vinylidene Intermediates

We report a new ruthenium-catalyzed cycloisomerization of unactivated cis-3-en-1-ynes, which produces substituted cyclopentadiene and related derivatives. The mechanism of this cyclization is proposed to involve a [1,5]-sigmatropic hydrogen shift of ruthenium-vinylidene intermediates on the basis of deuterium-labeling experiments.