Salen terminal ligands

Scheme 14. Possible fragmentation products upon CID of p-oxomanganese(IV)-salen complexes bearing two different terminal ligands...

The Jacobsen-Katsuki epoxidation reaction is an efficient and highly selective method for the preparation of a wide variety of structurally and electronically diverse chiral epoxides from olefins. The reaction involves the use of a catalytic amount of a chiral Mn(III)salen complex 1 (salen refers to ligands composed of the N,N -ethylenebis(salicylideneaminato) core), a stoichiometric amount of a terminal oxidant, and the substrate olefin 2 in the appropriate solvent (Scheme 1.4.1). The reaction protocol is straightforward and does not require any special handling techniques. 

These catalysts, 11-13, show good enantioselectivity ranging from 80 to 95% ee in the epoxidation of conjugated cfs-di- and tri-substituted olefins. Epoxidation of "good substrates such as 2,2-dimethylchromene derivatives proceeds with excellent enantioselectivity (>95% ee). Since the results obtained with these first-generation Mn-salen catalysts have been reviewed [21,33], only typical examples are shown in Table 6B.1. These reactions are usually carried out in the presence of donor ligand [34] such as 4-phenylpyridine A -oxide with terminal oxidants such as iodosylbenzene and sodium hypochlorite as described above. However, the use of some other terminal oxidants under well-optimized conditions expands the scope of the Mn-salen-... 

A titanium complex (1) with a salen ligand is an efficient catalyst for the enan-tioselective epoxidation of alkenes with hydrogen peroxide as the terminal oxidant. The participation of a titanium-peroxo species, activated by hydrogen bonding, in the reaction, has been postulated.73... 

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