Ethyl 2:2:4-trimethylcyclohexan-1-one-4-carboxylate, the preparation of which is now described, affords, on bromination followed by treatment with barium hydroxide, 1-hydroxy-3:5:5-trimethylcyclopentane-1:3-dicarboxylic acid. The reaction involves molecular rearrangement of the type previously observed by Wallach, Simonsen, and their co-workers. The product is probably the trans-modification of Aschan's α-hydroxyisofenchocamphoric acid, since, on dehydration with phosphorus oxychloride and pyridine, it gives 3:5:5-trimethylcyclopent-1-ene-1:3-dicarboxylic acid (dehydroisofenchocamphoric acid). This on catalytic reduction gives (±)-cis-isofenchocamphoric acid, which establishes the correctness of Semmler-Wallach formula for this acid. A direct synthesis of dehydrosisofenchocamphoric acid from ethyl 2:2:4-trimethylcyclopentan-1-one-4-carboxylate (Bardhan and Ganguli, J., 1936, 1852) by the action of hydrogen cyanide followed by dehydration and hydrolysis is also described.