|
New progress in the asymmetric epoxidation of olefins with chiral bioinspired manganese complexes was achieved by the researchers of State key laboratory for OSSO, LICP, CAS. They have designed and synthesized a novel series of chiral tetradentate N4 ligands together with their manganese complexes. With 1 mol% manganese catalyst loading, the enantioselective epoxidation of olefins proceeds with nearly full conversion and enantiomeric excess values of up to 89 % for the first time.
The asymmetric epoxidation of olefins is a very important organic transformation since the resulting enantiomerically pure epoxides are highly useful intermediates and building blocks. Many efforts have been dedicated to the development of chiral catalysts that can perform an asymmetric epoxidation reaction effectively. However, the chiral N4 manganese complexes previous research reported only exhibit low enantioselectivities. The present MnII complexes of chiral N4 ligands developed by our researchers are capable of achieving high enantiomeric excess in the catalytic asymmetric epoxidation. By comparison of [MnII(R,R-mcp)(CF3SO3)2] and new MnII complexes, it is clear that the size of the C7 and C7’ substituents is crucial to gain high asymmetric induction. To introduce proper groups on these positions will tune the steric bulk and electronic property of the ligands and result in significant improvement in enantioselectivity. The research indicates a conceptual strategy to improve the stereoselectivity of biologically inspired oxidation catalysis.
This work is financially supported by the Chinese Academy of Sciences and the National Natural Science Foundation of China (Org. Lett., Vol. 11, No. 16, 2009).
Abstract of the article published inOrg. Lett. |
