Palladium-catalyzed isomerization of methylenecyclopropanes in acetic acid.

[reaction: see text] Pd(PPh3)4-catalyzed isomerization of MCPs 1 in acetic acid proceeds smoothly at 80 degrees C in toluene to give the corresponding 1-substituted or 1,1-disubstituted dienes 2 in good to excellent yields under mild conditions. The plausible mechanism has been disclosed on the basis of a deuterium-labeling experiment.