Zusammenfassung The dye-sensitized photooxygenation of the title compounds leads by an “ene-reaction” mechanism to hydroperoxides with a shifted double bond which, treated by NaBH 4, give 1, 1-dimethyl-1-silacyclopent-4-ene-3-ol and 1, 1-dimethyl-1-germacyclopent- 4-ene-3-ol, respectively.