Oxidation of organic compounds with hydrogen peroxide has attracted attention for a long time and has been attributed to green chemistry. We used hydrogen peroxide in reactions with cyclic alcohols and observed unusual rearrangement reactions under ring enlargement giving new hydroperoxides and peroxides. [1][2][3] In this way we also obtained aliphatic primary geminal dihydroperoxides.[2] We report here on reactions of cyclic epoxyketones with hydrogen peroxide. Such epoxides are usually synthesised by the Weitz-Scheffer reaction, that is, by reaction of a,b-unsaturated ketones with H 2 O 2 under basic conditions.[4] We treated such products with 70 % H 2 O 2 in the presence of catalytic amounts of camphor sulfonic acid at room temperature.Substituted 6-ring epoxyketones 1 at the 3-position gave mixtures of products, interestingly consisting of geminal dihydroperoxides 2, dicarboxylic acids 3, carboxylic acids 4 and ketocarboxylic acids 5 (Table 1, Scheme 1).The geminal dihydroperoxides 2 show significant signals in the NMR spectra. [2,[5][6][7] Thus, the hitherto unkown ethane-1,1-dihydroperoxide (2 a) exhibits a signal at 107.9 ppm in the 13 C NMR spectrum and one typical hydroperoxide-H signal (intensity two protons) at 9.71 ppm in the 1 H NMR spectrum. In combination with the HR-ESI MS result, the structure of 2 a could be proven unambiguously. The geminal dihydroperoxide 2 a has the highest content of peroxide oxygen (68 %) relative to hitherto known organic peroxides and hydroperoxides.The so-called triacetone triperoxide (6; 43 % peroxidic oxygen) and methylhydroperoxide (7; [8] 66.7 %) were reported as highly explosive compounds. Despite the very high oxygen content compound 2 a is remarkably stable. It can be kept at room temperature for several days and at À20 8C for several weeks without decomposition. Thermogravimetric investigations (see Supporting Information) showed decomposition in the temperature range 60-130 8C with the highest decomposition rate at about 105 8C. Using differently substituted epoxyketones as reactants we were also able to isolate and characterise propane-1,1-dihydroperoxide (2 b), which is not yet described in literature, and to obtain benzylidenedihydroperoxide (2 c). The latter was previously described by using a different method from the reaction of benzaldehyde with H 2 O 2 .[ 4 [%] [b] 5 [%] [b]