Calcium peroxide diperoxohydrate (CaO2·2H2O2) is an environmentally friendly generator of singletoxygen (1O2, 1Δg) that can be used in organic synthesis as an alternative to the regular photochemicalmethod. This compound produces 1O2 in various solvents and can be easily recovered by filtrationfor further regeneration. Both monitoring of 1O2 luminescence at 1270 nm and specific trappinghave shown that CaO2·2H2O2 can be stored for several days at −80 °C and that the yield of 1O2 isequal to 25%. Oxidation of typical organic substrates in methanol or THF through [4 + 2] or [2 + 2]cycloaddition and ene reaction have been carried out on a preparative scale with total conversionand selectivity.