Polyfluorinated indans and tetralins are carbonylated under the action of CO/SbF5 at room temperature and atmospheric pressure. Perfluoroindan and its 4-CF3, 5-CF3, 5-CH3, 1,1-H,H derivatives add two CO molecules to form the corresponding dimethyl indan-1,1-dicarboxylates after methanolysis, and/or 1-hydroindan-1-carboxylic acids after hydrolysis. 1-X-Perfluoroindans (X[dbnd]CF3, C2F5, C6F5, H) and 1-X-perfluorotetralins (X[dbnd]C2F5, C6F5) add one CO molecule at the 1-position to give the corresponding 1-carbonyl fluorides. Reaction of the latter with methanol gives methyl esters, whereas hydrolysis is accompanied by decarboxylation. Perfluoro-2,3-dihydrobenzofuran under the action of CO/SbF5 gives both mono- and dicarbonylation products.