Ethyl 2 : 2 : 4-trimethylcyclopentan-1-one-4-carboxylate (Bardhan and Ganguli, J., 1936, 1853) condenses with ethyl cyanoacetate to give ethyl 4-carbethoxy-2 : 2 : 4-trimethylcyclopentylidenecyanoacetate. This is reduced catalytically to ethyl 4-carbethoxy-2 : 2 : 4-trimethylcyclopentylcyanoacetate, which on hydrolysis with hydrochloric acid gave 4-carboxy-2 : 2 : 4-trimethylcyclopentaneacetic acid. The last on pyrolysis yielded a ketone identical with (±)-isofenchone. On oxidation with potassium permanganate the synthetic ketone gives an excellent yield of (±)-cis- isofenchocamphoric acid. This synthesis supplies the final proof of the correctness of Semmler's formula for isofenchone.