The monocyclic terpene oxides, limonene oxide, and carvomenthene oxide have been reported previously to yield a variety of six-membered ring products by reaction with alumina or Lewis acid catalysts. It has been found that limonene oxide in the presence of zinc bromide rearranges with ring contraction to 1-methyl-3-isopro-penylcyclopentyl-1- carboxaldehyde and methyl (3-isopropenylcyclopentyl) ketone and isomerizes to ...
