My research plan focus on the development of chiral N,P-Ir catalyst. In our group, we designed and developed the chiral N,P-Ir catalyst for the asymmetric hydrogenation of enamines, vinyl phosphonates, vinyl-CF3, vinyl silanes, ?,?-unsaturated esters, enol ethers, heteroaromatic rings, vinyl fluorides and enol phosphinate.
In the first year, I have participated in the project “iridium-Catalyzed Asymmetric Hydrogenation of allylic alcohols via dynamic kinetic resolution”. We found that some racemic secondary allylic alcohols could be racemized by Ir-N,P- catalyst under standard conditions, and were obtained in good yield with excellent diastereoselectivities (up to 95/5) and enantioselectivities (up to 99%). We propose that carbocation formation could have occurred in the racemization process but this is not confirmed and the mechanism of the reaction is still under investigation.
Scheme 1 Dynamic kinetic resolution of allylic alcohol
Simultaneously, I worked on the asymmetric hydrogenation of tetrasubstituted olefins. Although the asymmetric synthesis of these compounds represents a considerable synthetic challenges due to the difficulties of controlling the formation of vicinal stereogenic centers, the N,P-Iridium catalyst in our group showed good yield and high enantiometic excess with wide substrates scope in benzene at 100 bar hydrogen pressure. In addition, we developed the method for synthesis of γ-lactone, which shows diverse range of biological activities.
Scheme 2 Asymmetric hydrogenation of tetrasubstituted olefins
Another part of the study is Ir-catalyzed subsequently asymmetric hydrogenation outside and inside the aromatic ring. We first created a chiral center outside the aromatic ring with high enantiomeric excess by our catalyst. Then, birch reduction of the newly formed products will provide optical pure diene/triene compounds, followed by the second asymmetric hydrogenation to create new chiral centers inside the ring. We are now exploring the substrates scope. In addition, we are also trying to utilize this strategy in total synthesis of bioactive molecules.
Scheme 3 Ir-catalyzed subsequently asymmetric hydrogenation
Currently, I am involve in design and synthesis of various new N,P-iridium catalyst and will investigate the newly synthesized catalyst for the asymmetric hydrogenation of substrates described above. Based on our previous result, I am planning to prepare a series of N,P-iridium ligand by varying heteroatom of the heterocyclic ligand or by varying substituents of the heterocycle. We expect that newly synthesized N,P-Iridium catalyst will be very useful for asymmetric hydrogenation and show good yield and excellent enantiomeric excess for different class of olefins.
Scheme 4 Synthesis of new ligand
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