The design, structural characterization, and evaluation of a unique class of 1,2,3-benzoxathiazine-based oxaziridines as potent O-atom transfer agents for catalytic C-H hydroxylation and alkene epoxidation are described. Turnover of this reaction is made possible by employing a diaryl diselenide cocatalyst and urea.H2O2 as the terminal oxidant. Oxidation of saturated hydrocarbons is strongly biased toward 3 degrees C-H bonds even in systems possessing a significantly greater number of methylene groups. In addition, the benzoxathiazine catalyst is effective for epoxidation of terminal and electron-deficient olefins. Collectively, these findings represent an important first step toward the advancement of general methodology for selective C-H oxidation.