Asymmetric olefin metathesis catalysts based on chiral extended N-heterocyclic carbenes with a bicyclic framework
Final Report Abstract
In summary, the project was focused on the synthesis of new chiral Grubbs-Hoveyda II catalysts based on chiral extended N-heterocyclic carbenes with a bicyclic framework. The carbene precursors were prepared from camphor as the chiral pool source and although only one chiral backbone in the carbenes was present, different sidearms in the ligands resulted in enantioenriched products in the catalytic reactions. It was found that the introduction of very sterical hindered sidearms is difficult. In addition, depending on the electronic features of the sidearms in the ligands an influence on the trans/cis selectivity was observed. In the catalytic asymmetric metathesis reactions, the highest ees were in a moderate range. Some analogues of these camphor-based carbene Grubbs-Hoveyda II catalysts had already proven to give asymmetric induction in asymmetric ring opening cross metathesis. Hence, a major investigation in this project was to carried out asymmetric ring-rearrangement metathesis (ARRM) reactions with the prepared enantiopure catalysts. In these reactions only a minor asymmetric induction was observed.
