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Conversion of a carbon–carbon double bond into a three-membered cyclic ether (an oxirane or epoxide) is epoxidation. An electrophilic oxygen atom is delivered to the alkene from a peroxy acid, a metal–oxo or metal–peroxo species, a dioxirane, or an ylide, forming two new C–O bonds in one operation. Chromium- and manganese–salen complexes promote alkene epoxidation through high-valent metal–oxo intermediates whose ligand environment controls enantioselectivity [1]. Homogeneous and heterogeneous catalytic asymmetric epoxidations generalize the same oxygen-atom transfer to a prochiral alkene under chiral catalysis [2]. Ylide-based epoxidation constructs the oxirane by addition of a sulfur or related ylide to a carbonyl, which is a complementary C–C/C–O route to the same ring rather than direct oxidation of an alkene [3]. The defining product is the epoxide; allylic oxidation, dihydroxylation, and aziridination are related atom-transfer reactions that install different three-membered rings or different oxidation patterns. Ring-opening of an already formed epoxide is a subsequent reaction, not part of the epoxidation event.
References
- Eoghan M. McGarrigle; Declan G. Gilheany; Chromium− and Manganese−salen Promoted Epoxidation of Alkenes. Chem. Rev. 2005, 105, 1563-1602. [CrossRef]
- Q.-H. Xia; H.-Q. Ge; C.-P. Ye; Z.-M. Liu; K.-X. Su; Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation. Chem. Rev. 2005, 105, 1603-1662. [CrossRef]
- An-Hu Li; Li-Xin Dai; Varinder K. Aggarwal; Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement. Chem. Rev. 1997, 97, 2341-2372. [CrossRef]
