ACID-CATALYSED acetolysis of a-acetyly-phthalimidoacetoacetic ester (I) yielded 1- phthalimidopentane-2: 4-dione (11), mp 129.5", in almost quantitative yield. The latter has not, so far as we are aware, been described previously, although Scheiber (Ber., 1909, 42,