Ruthenium-Catalyzed Cyclopropanation of Alkenes Using Propargylic Carboxylates as Precursors of Vinylcarbenoids

Intermolecular cyclopropanation reactions of various alkenes with propargylic carboxylates 1 are
catalyzed by [RuCl2(CO)3]2 to give vinylcyclopropanes 2 in good yields. The key intermediate of the
reaction is a vinylcarbene complex generated in situ by nucleophilic attack of a carbonyl oxygen of
the carboxylates to an internal carbon of the alkyne activated by the ruthenium complex. A variety
of transition-metal compounds other than the Ru compound can also be employed in this system.
Similar cyclopropanation proceeds with conjugated dienes as well to give trans-vic-divinylcyclopropane derivatives and cycloheptadiene derivatives 5, the latter being thermally derived from
the initially formed cis-vic-isomers via Cope-type rearrangement. The present reaction is chemically
equivalent to the transition metal-catalyzed cyclopropanation reaction using α-diazoketones as
carbenoid precursors.