Mechanism of Ru(II)-Catalyzed Rearrangements of Allenyl- and Alkynylcyclopropanols to Cyclopentenones.

A comparison study of the Ru(II)-catalyzed rearrangements of allenyl- and alkynylcyclopropanols to the corresponding cyclopentenones has been undertaken with the aid of an alkyl substituent on the three-membered ring. These ring expansion reactions proceed with exceptional regioselectivity irrespective of the cis/trans stereochemistry of the substituents on the three-membered ring. β-Carbon elimination is the common feature in the absence of a chelating group at the 4'-position in the alkyne chain.