EPOXIDATION CATALYST, ENANTIOSELECTIVE

Lakner FJ, Hager LP (1996) Chloroperoxidase as Enantioselective Epoxidation Catalyst An Efficient Synthesis of (R)-(-)-Mevalonolactone. J Org Chem 61 3923... 

CPO has been used occasionally in complex syntheses. An important application of CPO as an enantioselective epoxidation catalyst is the efficient synthesis of (R)-2-mevalonolactone (Scheme 2.26a) [270]. A survey of the literature revealed that the previous methods required many steps to produce the lactone, in low overall yield, with moderate ee, in addition to expensive starting materials. Meanwhile, a retro-synthetic analysis starting with an appropriately functionalized epoxide provided confidence that CPO could rescue the situation if used in the key stereogenic step. Another completed synthesis is depicted in Scheme 2.26b. Again, the epoxide is generated in high yield with conversion to (R)-dimethyl-2-methylaziridine-l,2-dicarboxylate, which may serve as a synthon for P-methylamino acids [283],... 

R,R)-N,N -Bis-(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino Manganese(lll) Chloride, a Highly Enantioselective Epoxidation Catalyst. 

For the epoxidation of a variety of olefins chiral Mn(III)-salen conq>lexes have been introduced by Jacobsen and subsequently Katsuki . These catalysts have emerged as the most enantioselective epoxidation catalysts uncovered to date. The system is particularly well suited for the epoxidation of c >disubstituted olefins and tiisubstituted olefins. Emm-epoxides are obtained with high enantioselectivities in the presence of an additional chiral quartemary ammoniiun salt . ... 

The design of viable, highly enantioselective epoxidation catalysts based on porphyrin ligands is confronted by the inherent difficulty associated with inducing dissymmetry from remote parts of an sp -hybridized coordination sphere, and the relative difficulties in constructing the chiral porphyrin rings. As research in this field has been the subject of an insightful review [90], only more recent developments will be covered here. 

Gross, Z., S. Ini, M. Kapon, and S. Cohen (1996). First utilization of a homochiral ruthenium porphyrin as enantioselective epoxidation catalyst. Tetrahedron Lett. 37, 7325-7328. 

Jacobsen EN, Zhang W, Mud AR, Ecker JR, Deng Li. Highly enantioselective epoxidation catalysts derived Irom 1,2-diami-nocyclohexane. J. Am. Chem. Soc. 1991 113 7063-7064. 

Brandes BD, Jacobsen EN. Highly enantioselective epoxidation catalysts derived from 1,2-diaminocyclohexane. J. Org. Chem. 1994 59 4378 380. 

In 1996, a fructose-derived ketone was identified by Shi and co-workers to be a highly reactive and enantioselective epoxidation catalyst for frtz 5-disubstituted and trisubstituted olefins." Good yields and high enantioselec-tivities can be obtained with 30 mol% of ketone 62 for a wide range of unfunctionalized ira 5-disubstituted and trisubstituted olefins (Scheme 35.16). The epoxidation is typically performed at pH around 10.5 by adding either potassium carbonate or potassium hydroxide into the... 

Lakner EJ, Hager LP. Chloroperoxidase as enantioselective epoxidation catalyst an efficient synthesis of (R)-(—)-meva-lonolactone. i. Org. Chem. 1996 61 3923-3925. 

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