Effect of beta-Substituents on the Regioselectivity of the Diazomethane Ring Expansion of alpha-Methyl-alpha-methoxycyclobutanones to Cyclopentanones.

The ring expansion of 22 differently beta-substituted alpha-methyl-alpha-methoxycyclobutanones by diazomethane was studied. Migration of the less-substituted alpha-carbon was favored with the single exception of a very sterically hindered beta-benzyloxy beta-substituent.