Electron-rich alkenes dioxirane epoxidation

Electron-rich alkenes are the more reactive jr-bond snbstrates towards epoxidation by the electrophilic dioxiranes Some typical examples of these oxidations are snm-marized in Scheme 2. Since the resnlting epoxides are nsnally hydrolytically and ther-molytically qnite labile, snch oxidations are best carried ont with isolated dioxiranes. For example, the 8,9 epoxide of the well-known aflatoxin B, postnlated as potent carcinogen in the oxidative metabolism of this natural product, escaped numerous efforts to prepare it by conventional epoxidations because of its sensitivity towards hydrolysis . The synthesis of this labile epoxide was readily accomplished by employing a solution of the isolated DMD at room temperature (equation 2), and its mutagenicity unequivocally... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

---