decomposition of dioxiranes to singlet oxygen is a unique problem associated with dioxirane heteroatom oxidations. Although chiral dioxiranes do not provide the same levels of enantioselectivity as other protocols, such as Kagan's sulfoxidation system, complexation to a chiral transition metal complex followed by oxidation affords optically active sulfoxides with good enantioselectivity. Oxidation of arenes and cumulenes leads initially to epoxides. These substrates are resistant to many epoxidation reagents, including oxaziridines, hydrogen peroxide, and manganese oxo compounds. Organometallic oxidants also react sluggishly with these compounds, with the exception of methyltrioxorhenium. Peracids also react with arenes and cumulenes, but cannot be employed with substrates containing acid-sensitive functionality. The direct oxidative functionalization of C-H bonds is an ongoing problem in oxidation chemistry. Among metal-free systems, dioxiranes are the best oxidants for the conversion of C-H bonds to alcohols or carbonyls. However, some catalytic transition-metal systems, such as White's palladium-sulfoxide system, are able to oxidize C-H bonds selectively. Experimental conditions and procedure Typical conditions Dioxiranes are volatile peroxides and should be handled with care in a well-ventilated fume hood. Inhalation and skin exposure should be strictly avoided. As many dioxirane oxidations depend subtly on reaction conditions, care should also be taken to optimize reaction parameters such as equivalents of oxidant and temperature. Hydroxylic and ethereal solvents should never be used in reactions of dioxiranes, as competitive oxidation of the solvent will take place. Preparation of TFD A 150 mL, five-necked round-bottomed vessel is equipped with a mechanical stirrer, an air-cooled straight condenser loosely packed with silanized glass wool, a solids addition funnel, a gas inlet tube extending into the reaction mixture, and a thermometer. The air condenser is connected laterally to the top entry of an efficient-jacketed spiral condenser cooled at −75 °C (dry ice/acetone); the bottom exit of this condenser is fitted to a two-ways fraction-collector adapter carrying two 50 mL receiving flasks, also cooled at −75 °C. In succession to the adapter, two cold traps are placed, the first cooled at −75 °C, and the second at liquid nitrogen temperature. The main vessel is charged with NaHCO3 (1.5 g) and Na2H2EDTA (0.5 g) dissolved in 15 mL of bidistilled water, and cooled at 2–5 °C. To this 20 g (0.179 mol) of 1,1,1-trifluoro-2-propanone is added, and mechanical stirring is initiated. Solid potassium peroxomonosulfate (0.081 mol, 25 g of Curox triple salt) is quickly added (1–2 min) to the reaction vessel, while passing