Abstract The paper describes regiospecific synthesis of 4, 4-and 5, 5-disubstituted 4, 5- dihydro-6H-canthin-6-ones III and XVIII, starting from half-esters of 2, 3-disubstituted succinic acids, V and XIV. The formation of the anomalous 5, 5-disubstituted canthin-4, 6-diones XVII is ascribed to oxidation of the intermediate XIX. The 1 H NMR spectra of the compounds prepared are discussed.
