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Adolfsson, H., Science of Synthesis, (2008) 37, 251.
A breakthrough in the area of asymmetric epoxidation came in the beginning of the 1990s when the groups of Jacobsen and Katsuki more or less simultaneously discovered that chiral manganese–salen complexe 23 catalyzed the enantioselective formation of epoxides (Scheme 28).[87–89] The discovery that simple nonchiral manganese–salen complexes could be used as catalysts for alkene epoxidation was already established about five years earlier, and the typical terminal oxidants used with these catalysts closely resemble those of the porphyrin systems.[54] In contrast to the titanium-catalyzed asymmetric epoxidation discovered by Sharpless, the manganese–salen system does not require precoordination of an allylic or homoallylic alcohol to the catalyst, hence unfunctionalized alkenes can be efficiently and selectively oxidized. The enantioselectivity has been shown to be highly sensitive toward the substitution pattern of the alkene substrate. Excellent selectivity (>90% ee) is obtained for aryl- or alkynyl-substituted terminal, Z-disubstituted, and trisubstituted alkenes, especially using the second-generation catalysts (here exemplified by complex 24),[90] whereas E-disubstituted alkenes are epoxidized with low rates and low enantiomeric excesses (< 40%) (Scheme 29).
Meeeee 88 Meeeeeeee–eeeee Meeeeeeee[88,88]
Meeeee 88 Meeeeeeeeee ee Meeeeee Meeee e Meeeeeeee–eeeee Meeeeeee[88]
Me eeee eeeeeee, eee eeeeeeeee eeeeeeee–eeeee eeeeee eeeeeeeee ee Meeeeee 88.8.8.8.8.8 eeeeee ee eeee eeeeeeeeee ee eee eeeeeeeee eeeeeeeeeee eeeeeee eeee eeeeeeeeeeeeeeeeee eee ee eeeeeeee ee eee eeeeeeeeeee ee eee “eeeeeeeee” M-eeeeeeeeeeeee eeeeeee. Meeeeeeeeeee, eee eee ee eeeeeeee 88 ee eeeeeeeeee eeeeeeeeeee ee eeeeeeeee eeeeeeeeee eee eee eeeeeee ee eee eeeeeeeeee ee eeeeeeeeee eeeeee eeeeeeee eee ee eeeee ee eee eeeeeeeeee eeeeeeeeee ee eee MMM-eeeeeeee eeeeeeeee eeeeeeeee.[88] Mee ee eee eee eeeee ee eeee eeeeeee ee eee eeeeeeeeeeeeeeee eeeeeeeeeee ee 8M-eeeeee ee (8eM,8eM)-8,8e-eeeeeee-8eM-eeeeee[8,8-e]eeeeeee (Meeeee 88).
Meeeee 88 Meeeeeeeeee ee Meeeeeeee[88]
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Meeeee 88 Meeeeeeee eee Meeeeeeeeeeeeeee ee eee Meeeeeeee–eeeee Meeeeeeeeee: Meeeeeeee Meeeeeee Meeee[88]
Meeeeee, eeeeeeeeeeee eeeee eeeeeee eeeeeeeeee eeeeee ee eeeeeeeeeee eeee eeeeeeeee eeeeeeeee eeeeeee eeeeeee eeee eee eeeeee ee eeeeeeeeeeeeeeeeee eeeee eeee ee eeeeee eeeeeeee eeee eee eeee ee eee eeeeeeee eeee, ee eeeeeeee ee Meeeee 88.[88] Meeeeeeee ee eeee eeeee, eee eeeeeeee eeeeeee eeee eeeeee eeee eeeeeeeeeee ee eee eeeeeeee eee ee eeeeeeeeee ee: (8) Mee eeeeeeeeeeeee eeeeeeeeee eeeee ee eee eeeeeee eeeeee eeee eeeeee e eeeeeee ee eee eeeeee eee eeeeeee eeeeee e eeeeee eeeeee; (8) eee eee-eeeeee eeee eeee eeee eeeeee eeeeee ee e eeee-ee eeeeeeee eeee eee ee eee eeeeeeee eeeee; (8) eeeeee ee eee eeeeee eeee eee eeeee ee eeeeeeeeeee eeeeeeee ee eeeee eeeeee ee eee 8,8'-eeeeeeee ee eee eeeeee, eee ee eeeeeeee eeeeeeeee ee Meeeee 88 eee eeeeeeeeee ee ee eeeeeeeeee ee eeeeeeeeeeeee 8 eeee·eee−8.
Meeeee 88 Meeeeeeee eee Meeeeeeeeeeeeeee ee eee Meeeeeeee–eeeee Meeeeeeeeee: Meeeeeee Meeee Meeee ee Meeeeeeeeee[88]
Mee eeeeeee eeeeeee eeee ee eeeeeeeee–eeeee eeeeeeeeee eeeeeeeeeeee ee eeeeee eeeeeeeeeeee; eeeeeee, eeee ee eee eeeeee ee Meeeeeeee eee Meeeeee eee eeeeee ee eee eeeeeeeeeee ee eeeeeeee eeeeeeee eeeee eeeeeeee.[88,88] Meeeeeeee eee eeeee eeee eeeeeeeee eeeeeeeee eee eeeeeee eee eee eeeeeeeee ee eee eeeeee eeeeeeeeeeee eeeeeeeeeeeee, eee e eeeeeeeee eeeeeeee 88 eeee ee eeeee ee e eeeee eeeeee eeeeeeeeeeeee e eeeeeee eeeeeeeee eee eeee eeee eee eee eeeeeeeeee eeeeeeeeeee eeeee eeeeeee eeeeeeee eeeeeeee (Meeeee 88). Meeeee eee eeeeeeeeeeeeeeeeee ee eee, eeeeeee, eeeee eee eeeeee eeeeeeee eeee eeeee eeeeeeee eee eeee. Meeeeeeee–eeeee eeeeeee 88 eee eeee eeee eeee eee eeeeeeeeeee eeee eeeeeeee eeeeeeee.
Meeeee 88 Meeeeeeee–eeeee Meeeeeeeeee Meeeeeeee Meee ee Meeeeeeeeee eeee Meeeeeee Meeeeeee[88,88]
Me eee eeee ee Meeeeee, M-eeeeeeeeeeeeeee ee eeeeeee ee ee eeeeeeee ee eee eeeeeeeeeee ee e 8M-8-eeeeeeeeee eeeeeeeeee eeeee eee eeeeeeeeee eeeeeeee eeeeeeeee–eeeee eeeeeeee 88 (Meeeee 88). Me eee eeeeeeeee eeeeeeeeeeeee (8.8 M), eee eeeee ee eeee 88%; eeeeeee, eeeeeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeee eeeee eeeeeeeeeeeee eeee eeeeeee eeeeeeeee. Meeeeeeeeeeee, eeeee eeeeeeeeee eee eee eeeeeeee ee eee eeee eeeee eee eeeeee ee eeeeeeeeeeeeeeeeee.
Meeeee 88 Meeeeeeeee Meeeeeeeeee ee e 8M-8-Meeeeeeeee[88]
Meeeeeäeeee eee eeeeeeee ee eee eee ee eeeeeeee eeeeeee (88 eee%) ee ee eeeeeeee eeeeeeee eeee eee Meeeeeee eeeeeeee 88 ee eee eeeeeeeee–eeeee eeeeeeee 88 eee eee eeeeeeeeeee ee e eeeeee ee eeeeeee eeee eeeeeee eeeeeeee eeeeeeee ee eee eeeeeeee eeeeeee.[88] Me eeeeeee, eeee eeeeeeee eeeeeeeee eeeeeeee ee 88–88% eeeee eeee eeeeeeeeeeeeeeeeee ee ee 88%; eeeeeee, eeee e eeeeee eeeee ee eeeeeeeeee eee eeee eeeeeeee. M eeeee eeeeeee eeee eeeee eeeeeee eeeeeeee eeeeeeee ee eee eeeeeeeee–eeeee eeeeeeeee eeeeeeeee ee eeeeeeeeee eeee eeeeeeeee-eeeeeeeee eeeeeee eeeeeeeeeeeee eee eeeeeeee eeeeeeeeeeee eee ee eee eeeeeeee ee eeeee. Meeeeeeee eeeeeeee eeeeeeee, eeeeee ee eee eeee ee eee eeee–eeeeeeee eeeeeeee eeeeee (MMM) ee eee eeeeeeeeeeeeeeeeee eeeee–eeeeeeee eeeeeeee eeeeee, eee eeee eeeeeeee ee eeeeeeeeee eeee eeeeeee (Meeeee 88).[888–888] Meeeeeee eeeeeee eeeee eee eeeeeeeeeeeeeeeeee eee ee eee eeeee ee eeee eee ee eeeeeeee eeeee eeeeee eeeeeeeeeeee, eee eeeeeeee eeeeeee ee eeeee eeeeeeeeeeeee eeeeee, eee eee eeeeeee ee eeee ee eeeeeeeeeeeeeeeeee eeeee eeeeeeeeeee ee eeeeeeeeee eeeeeee.
Meeeee 88 Meeeeeeeeeeeeeee Meeeeeeeeee ee 8,8-Meeeeeeeeeeeeeeeee Meeee Meeeeeeee-(MMM)–eeeee Meeeeeeee[88,88–888,888]
e 8-MMMM = 8-eeeeeeeeeeeeee M-eeeee; MMM = M-eeeeeeeeeeeeeeee M-eeeee; MM = eeeeee eeeeeeeee.
e Me eeee eeee, eee eeeeee eeeeeee ee eeeeeeeeeeee eeee eeeeee ee eeee eeeee ee eee eeeeeeeeeee eeeeeeee.
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References
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) M 88e, 8888.
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