Photoinduced single electron transfer (SET) reactions of α,β-epoxy ketones have been studied using alkylamine electron donors. Irradiation of chalcone epoxide 1 with triethylamine (TEA) afforded β-diketone 2 and β-hydroxy ketone 3. Photoreaction of 1 with TEA in MeOH resulted in a slightly increased product ratio (3/2) compared with that in MeCN. When 1,4-diazabicyclo[2.2.2]octane (DABCO) was used instead of TEA, a decrease in the yield of 3 was observed. Only 2 was obtained on irradiation of a solution of 1 in TEA and MeCN containing LiClO4. Studies of photoreactions of dypnone epoxide 9, benzoylisopropylethylene epoxide 12, and acrylophenone epoxide 15 indicate that the nature of β-substituent also influences the product distribution. It was also found that 1,6-bis(dimethylamino)pyrene (BDMAP) sensitizes the photoreaction of 1 in the presence of TEA to produce 2. Based on the results obtained, a reaction mechanism involving selective Cα–O bond cleavage of intermediate α,β-epoxy ketone anion radicals is proposed. © 1991, American Chemical Society. All rights reserved.