Stereoselective Access to Conjugated and Cross-Conjugated Dienoates by Rh- and Ru-Catalyzed Isomerizations of Vinylcyclopropanes

Two complementary catalytic protocols
for the isomerization of
stereoisomeric mixtures of vinylcyclopropanes are described. A commercially
available cationic rhodium complex provides access to conjugated dienoates
in high yield with excellent stereocontrol. The combination of a bisphosphine
ligand and a ruthenium precatalyst affords cross-conjugated dienoates
via a formal 1,3-ring opening. The products are obtained with moderate
to high stereoselectivity. The ability of each type of dienoate to
engage in [4 + 2] cycloaddition reactions has been demonstrated.