Electron transfer-induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluoroborate (TPT) in cyclopentanone resulted in the diastereoselective formation of 2,5-dioxaspiro[4,4]- nonanes through Cα-O bond cleavage and following nucleophilic attack of cyclopentanone to radical cation intermediates. The readiness for ring opening is influenced by the nature and the location of the additional s`ubstituent on the α-epoxyketones.