Jacobsen epoxidation
Jacobsen epoxidation | |
---|---|
Named after | Eric N. Jacobsen
|
Reaction type | Ring forming reaction |
Identifiers | |
Organic Chemistry Portal | jacobsen-katsuki-epoxidation |
RSC ontology ID | RXNO:0000686 |
The Jacobsen
Several improved procedures have been developed.[4][5][6]
A general reaction scheme follows:[7]
History
In the early 1990s, Jacobsen and Katsuki independently released their initial findings about their catalysts for the enantioselective epoxidation of isolated alkenes.[1][3] In 1991, Jacobsen published work where he attempted to perfect the catalyst. He was able to obtain ee values above 90% for a variety of ligands. Also, the amount of catalyst used was no more than 15% of the amount of alkene used in the reaction.[2]
General features
The degree of enantioselectivity depends on numerous factors, namely the structure of the alkene, the nature of the axial donor ligand on the active oxomanganese species and the reaction temperature. Cyclic and acyclic cis-1,2-disubstituted alkenes are epoxidized with almost 100% enantioselectivity whereas trans-1,2-disubstituted alkenes are poor substrates for Jacobsen's catalysts but yet give higher enantioselectivities when Katsuki's catalysts are used. Furthermore, the enantioselective epoxidation of conjugated dienes is much higher than that of the nonconjugated dienes.[8]
The enantioselectivity is explained by either a "top-on" approach (Jacobsen) or by a "side-on" approach (Katsuki) of the alkene.
Mechanism
The mechanism of the Jacobsen–Katsuki epoxidation is not fully understood, but most likely a manganese(V)-species (similar to the
The radical intermediate accounts for the formation of mixed epoxides when conjugated dienes are used as substrates.[8]
Dimethyldioxirane]] can be used as a source of O atomes.DMD of a chiral metal catalyst followed by epoxidation, or (2) epoxidation by chiral dioxiranes, which are generated in situ from a catalytic amount of ketone and a stoichiometric amount of a terminal oxidant).
References
- ^ .
- ^ .
- ^ .
- .
- .
- .
- ^ "Jacobsen Epoxidation". Organic Chemistry Portal. Retrieved 2009-09-22.
- ^ .
- ^ Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y. J. Am. Chem. Soc. 1997, 119, 11224.
- ^ Lévai, A.; Adam, W.; Fell, R. T.; Gessner, R.; Patonay, T.; Simon, A.; Tóth, G. Tetrahedron 1998, 54, 13105.