Acyloxyl radicals RC(O)O* (with R = alkyl, aryl) could be trapped through addition to cyclic and open-chain alkynes, where they were found to act as a donor of oxygen atoms. Mechanistically, this radical oxygenation proceeded through a transannular or intramolecular, respectively, radical cyclization cascade, which was finally terminated by release of an acyl radical RC*(O). The reaction led to stereoselective formation of cyclized products, which contained a carbonyl group at the former site of the alkyne triple bond.