Acid-catalyzed rearrangement of 3-methylene-2,2,4,4-tetramethylcyclobutanone (1) gave the γ-lactone of 2,2,3,4-tetramethyl-4-hydroxyvaleric acid. Reaction of 2,2,4,4-tetramethylcyclobutane-1,3-dione (5) with PPA gave diisopropylketone with evolution of carbon dioxide. Acylium ions are postulated as intermediates in both these reactions.