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Hydrolytic Kinetic Resolution of Epoxides Using Polymer-Supported Cobalt Catalyst
X. Zheng, C. W. Jones, M. Weck*
Georgia Institute of Technology, Atlanta and New York University, USA
19 March 2008 (online)
A polymer-supported Co(III)-salen complex was synthesized and found to be highly effective for the HKR of a variety of racemic epoxides. Thus, etherification of styrene precursor 1 with benzyl chloride 2 gave the salicyl aldehyde 3. Schiff base condensation of diamine 4 with 3,5-di-tert-butyl-2-hydroxybenzaldehyde 5 followed by the reaction of the HCl-protected amine with aldehyde 3 afforded the salen monomer 6. The polymer-supported salen ligand 7 was obtained via polymerizaion of the monomer 6 with AIBN. Complexation of polymeric 7 with Co(OAc)2 gave Co(II)-salen complex 8, which was oxidized with air to afford the Co(III)-salen complex 8-OAc. The HKR reaction of various racemic epoxides was carried out in the presence of complex 8-OAc to give the corresponding R-enantiomers in 43-46% yield with 99% ee.