Selective Epoxidation of Olefins by Perfluoro-cis-2,3-dialkyloxaziridines¹

Abstract

Alkyl-substituted olefins are epoxidized by perfluoro-cis-2,3-dialkyloxaziridines under particularly mild conditions. Electron deficient substrates (e.g. alpha,beta-enones) can also be epoxidized, and the more electron poor the double bond is, the more severe the reactions conditions become. The epoxidation is chemoselective (secondary alcohols and their ethers do not interfere), site selective (the monoepoxide of a diene can be obtained), and stereoselective (cis-alkenes afford cis-epoxides). Various complex and polyfunctional substrates of natural origin (monoterpenes, sesquiterpenes, steroids) have been transformed effectively.

Synthesis of Fluorinated Tricyclic Scaffolds by Intramolecular [2+2] Photocycloaddition Reactions

“…An initial set of experiments was performed with tetronate 2 derived from commercially available 3,4,4-trifluorobut-3-enyl bromide. Despite the fact that the trifluoro-substituted alkene is extremely electron-poor, [10] it did successfully add to the photoexcited tetronate at l = 254 nm in isopropanol as the solvent (Table 1, entry 1). A further modification of the solvent revealed that diethyl ether (Table 1, entry 5) was superior to tert-butanol (entry 2), dichloromethane (entry 3), or acetonitrile (entry 4).…”

“…Scheme 3. Intramolecular [2+2] photocycloaddition of 2,2-difluorobut-3-enyl tetronate (10) to the respective difluorinated product 11. yield). Both compounds were subjected to an intramolecular [2+2] photocycloaddition at l = 254 nm in diethyl ether as the solvent.…”

Catalytic Oxidative Processes in Steroid Chemistry: Allylic Oxidation, β-Selective Epoxidation, Alcohol Oxidation and Remote Functionalization Reactions

“…A new system consisting of KMnO 4 /Fe(ClO 4 ) 3 .nH 2 O has recently been reported to afford these epoxides in high yields in the presence of NaH 2 PO 4 .3H 2 O [69]. On treatment with perfluoro-cis-2,3-dialkyloxaziridine, several 3 -substituted-5 -steroids produced the 5 ,6 -epoxides as major products, whereas cholesterol 26 and stigmasterol 33 mainly led to the 5 ,6 -epoxides [70].…”

Synthesis of Fluorinated Tricyclic Scaffolds by Intramolecular [2+2] Photocycloaddition Reactions

“…Despite the fact that the trifluoro-substituted alkene is extremely electron-poor, [10] it did successfully add to the photoexcited tetronate at l = 254 nm in isopropanol as the solvent (Table 1, entry 1). Despite the fact that the trifluoro-substituted alkene is extremely electron-poor, [10] it did successfully add to the photoexcited tetronate at l = 254 nm in isopropanol as the solvent (Table 1, entry 1).…”

“…Intramolecular [2+2] photocycloaddition of 2,2-difluorobut-3-enyl tetronate (10) to the respective difluorinated product 11. Intramolecular [2+2] photocycloaddition of 2,2-difluorobut-3-enyl tetronate (10) to the respective difluorinated product 11.…”