A series of 3-methylenecycloalkanones with ring sizes 7-10 has been prepared and subjected to base-catalyzed isomerization. Equilibrium between these exocyclic isomers and the corresponding 3-methyl-2-cycloalkenones and 3-methyl-3-cycloalkenones was reached in the 7-and 8-membered rings. The presence of the β-methyl shifts these equilibria toward the Δ2 isomer in each ring relative to the unsubstituted compounds and to ...