Iminium Salt‐Catalysed Asymmetric Epoxidation using Hydrogen Peroxide as Stoichiometric Oxidant

Abstract

Iminium salt organocatalysts can provide high selectivity and high efficiency in catalytic asymmetric epoxidation. They are normally used in conjunction with Oxone as the stoichiometric oxidant. Oxone, however, has limited stability and is insoluble in most organic solvents; we report here for the first time the development of a reaction system driven by hydrogen peroxide as the stoichiometric oxidant, involving an unusual double catalytic cycle

Recent Advances in Iminium‐Salt‐Catalysed Asymmetric Epoxidation

“…21 Olefin Epoxide yield / % % ee 84 92 96 97 65 89 Table 3. Asymmetric epoxidation of representative olefins using catalyst (27) Katsuki reported some excellent enantioselectivities for the catalytic asymmetric epoxidation 23 The different mechanisms proposed by Jacobsen and Katsuki account for the enantioselectivity observed. Lineker has also discussed the mechanistic aspects of the manganese-salen catalysed epoxidation.…”

“…The Jacobsen-Katsuki epoxidation of alkenes involves a manganese-salen based catalyst Further probing of the ligands surrounding the manganese metal centre yielded catalyst (27) ( Figure 4), showing further increases in enantioselectivity. Jacobsen tested other oxidants, including commercial bleach, and found that epoxidation reactions at 4 °C yielded enantioselectivities above 90% ee for selected olefins (Table 3).…”

“…Page has shown that a range of oxidants can be implemented in the catalytic iminium-salt mediated asymmetric epoxidation of olefins, including Oxone™, 25 sodium hypochlorite, 26 hydrogen peroxide, 27 and, most recently, tetraphenylphosphonium monoperoxysulfate (TPPP) under non-aqueous conditions. 16,17,18,28 Di Furia first reported the synthesis of TPPP in 1994.…”

“…(>96:4) and high enantioselectivity (>80 %) (Scheme 11). 27 The Jacobsen-Katsuki epoxidation has recently been utilized in the synthesis of the tetrasubstituted dihydroquinoline portion of Siomycin D 1 33 (related to peptide antibiotics) by Hashimoto. Epoxidation of the double bond at the C7-C8 position gave epoxide 32 in 43% yield and 91% ee (Scheme 12).…”

Activation of Hydrogen Peroxide by Diphenyl Diselenide for Highly Enantioselective Oxaziridinium Salt Mediated Catalytic Asymmetric Epoxidation

“…6 For example, epoxidation of cis-alkene 1 affords the corresponding epoxide 2 with 97% ee when employing iminium salt 3 (Scheme 3). 7 This system has since been used for the highly enantioselective total syntheses of levcromakalim [(-)-cromakalim], 7 (−)-(3'S)-lomatin, 8 (+)-(3'S,4'R)-transkhellactone, 8 We have also reported the use of hydrogen peroxide- 10 and sodium hypochlorite-11 driven systems for asymmetric oxaziridinium salt-mediated epoxidation. Both systems suffer from reduced rates of reaction and lower ees when compared to the original oxonemediated processes.…”