Katsuki-type salen ligand

The unsymmetrical analog of a Katsuki-type salen ligand was attached to Merri-field s resin (1% cross-Hnked) yielding a catalyst (22) (Fig. 4.3) which showed good efficiency and selectivity in the asymmetric epoxidation of 1,2-dihydronaphtalene with good performance after several recycling steps [81]. Related complexes (23) immobilized on silica were recently disclosed by Seebach and coworkers (Fig. 4.3) [82]. 

Smith and Liu <02CC886> have immobilized a Katsuki-type salen ligand by an ester linkage to Merrifield s resin to produce catalyst 7. In a test epoxidation of 1,2-dihydronaphthalene (8)... 

Only a few years after the development of the homogeneous chiral Mn(salen) complexes by Jacobsen and Katsuki, several research groups began to study different immobiUzation methods in both liquid and soUd phases. Fluorinated organic solvents were the first type of Uquid supports studied for this purpose. The main problem in the appUcation of this methodology is the low solubility of the catalytic complex in the fluorous phase. Several papers were pubUshed by Pozzi and coworkers, who prepared a variety of salen ligands with perfluorinated chains in positions 3 and 5 of the saUcyUdene moiety (Fig. 2). 

Kinetic resolution in the catalytic conversion of racemic chloro propanols to optically active epoxides has been achieved by use of a chiral Co(salen) type complex in combination with K2CO3. Although enantioselectivity was modest (< 35 % ee), this first use in asymmetric epoxide formation of the chiral ligand system that was later brought to fame through the Jacobsen-Katsuki asymmetric epoxidation is noteworthy [56,57]. When applied to the prochiral l,3-dichloro-2-propanol, asymmetric induction of up to ca. 60 % ee was achieved (Sch. 8) [58]. 

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