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theses

Asymmetric catalysis has been playing an important role in modern synthetic chemistry. In the past decades, chiral ligands especially phosphorus chiral ligands, have demonstrated their power in transition metal catalyzed asymmetric reactions. New chiral ligands with high efficiency, selectivity and generality are always the key for the campaign of asymmetric reactions. In this dissertation, we will focus on design of new chiral phosphorus ligands and their applications in rhodium-catalyzed asymmetric hydrogenation and hydroformytation. In chapter 1, the air stable bisphosphole BIBOP ligand was applied in asymmetric hydroformylation, the new rhodium based catalytic system was demonstrated to be very effective for vinyl acetate, allyl alkenes and styrene derivatives. A new synthetic route for a chiral δ-lactone via asymmetric hydroformylation was established. Computational studies were conducted for a deeper insight of the reaction mechanism. In chapter 2, a ligand library was screened for achieving rhodium catalyzed asymmetric hydroformylation of challenging 1,1-disubstituted alkenes. The BIBOP ligand successfully hydroformylated 1-(trifluoromethyl)-ethenyl acetate into a very useful precursor for drug synthesis, with good enantioselectivity. A branched product favoring approach was discovered for hydroformylation of α-(trifluoromethyl) styrene. Up to 68% ee was achieved with DuanPhos . Chapter 3 discussed the application of a novel cooperative catalyst system in asymmetric hydrogenation. Indole derivatives were hydrogenated via hydrogen bonding, with excellent enantioselectivity. The mechanistic studies supported a proton mediated tautormerization-hydrogenation sequence. Dimerization of ZhaoPhos was proposed for explaining the observed nonlinear effect.

ETD_8021

Ph.D.

Includes bibliographical references

by Renchang Tan

doi:10.7282/T3Z322JK

ETD doctoral

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