Mechanistic Study on Asymmetric Oxidations with Metallosalen Complexes as Catalysts and Exploitation of New Metallosalen Complexes

点击翻译按钮获取中文摘要

Metallosalen Complexes are excellent catalysts for asymmetric oxene and carbene transfer reactions but our understanding of the mechanism of asymmetric induction is still immature. However, knowledge on the mechanism is indispensable for understanding the stereochemistries of the asymmetric reactions and developing new type of highly efficient asymmetric reactions.Although salen ligand had been recognized to have a planar structure, the analysis of stereochemistry in the ylide formation of sulfide using chiral (salen)cobalt complex suggested that the salen ligand had not a planar but stepped structure. This finding on the ligand-conformation was strongly supported by realizing as asymmetric epoxidation with achiral (salen)manganese complexes as catalysts in the presence of chiral axial ligands. Furthermore, X-ray analysis of chiral (salen)manganese complexes proved that the salen ligands adopt stepped conformation. Basing on these findings, we succeeded in an efficient kinetic resolution of allene compounds and asymmetric hydroxylation of benzylic C-H bonds.In addition to these results, unique asymmetric cyclopropanation was also developed by employing nitroso (salen) ruthenium complexes. Though the ruthenium complexes are catalytically inactive, photo-irradiation makes them active. Furthermore, the complexes are expected to have highly pliable structure basing on the X-ray analysis of the complex. Taking advantage of high pliability of the ruthenium complex, we could controlled the ligand conformation by choosing solvent and achieve for the first time highly cis- and enantio-selective cyclopropanation.