Abstract: Dioxiranes are important oxidants for organic reactions such as epoxidation, heteroatom oxidation and oxygenation of C-H bonds. We have developed a mild and general method for epoxidation of olefins using dioxiranes generated in situ from ketones and Oxone. This method has not only extended the synthetic utility of dioxiranes, but also allowed us to discover a series of novel cyclic ketones for catalytic oxidation. In particular, we have demonstrated the potential of chiral ketones for catalytic asymmetric epoxidation of trans-olefins and trisubstituted olefins. We have also explored the potential of ketones in catalyzing oxidation of unactivated C-H bonds and decomposition of peroxynitrite.