Chapter 1. Methods for highly enantioselective Cu-catalyzed asymmetric conjugate additions of dialkylzinc reagents to unsaturated furanones and pyranones are presented. Transformations are promoted by a chiral peptide-based ligand in the presence of an appropriate Cu-salt. In order to carry out additions to a broad range of substrates, a small family of chiral peptide based ligands was utilized. The synthesis, characterization and use of air-stable Cu-peptide complexes is also presented.*
Chapter 2. New methods for the highly enantioselective formation of all-carbon quaternary stereogenic centers through catalytic asymmetric conjugate additions of dialkyl- as well as diarylzinc reagents are summarized. As introduction to Cu-catalyzed asymmetric conjugate addition to prepared all-carbon quaternary stereogenic centers is presented. For reactions involving unactivated cyclic β-substituted unsaturated carbonyls, a phenoxy-based N -heterocyclic carbene (NHC) ligand was found to optimal. Additions of diorganozinc reagents to cyclic unsaturated γ-ketoesters, however, required the use of a sulfonate-based NHC to provide the desired products efficiently and in high enantiomeric purity. The practicality of the method is demonstrated though the in situ preparation and use of diorganozinc reagents. Representative functionalizations of the enantiomerically enriched enolate are also included.*
Chapter 3. An enantioselective total synthesis of diterpenoid natural product clavirolide C is presented. The total synthesis requires 17 steps (longest liner) and provides the target compound in 3.5% overall yield. These studies have led to the development of a new method for the synthesis of all-carbon quaternary stereogenic centers though Cu-catalyzed ACA of trialkylaluminum reagents to β-substituted cyclopentenone derivatives. Additional features of the synthesis include: (i) Cu-catalyzed asymmetric conjugate addition of dimethylzinc to an unsaturated lactone; (ii) stereoselective aldol addition between an aliphatic-based aldehyde and a cyclopentenone-derived enolate; (iii) the synthesis of an 11-membered ring though catalytic ring-closing metathesis.*
Chapter 4. Several route for the synthesis of sulfonate-based NHC complexes are presented. In the course of these studies, a new method for the preparation of imidazolinium salts was discovered. Mechanistic studies, carried out to understand the details of the imidazolinium salt formation, eventually led to an improved synthesis. Physical properties of the sulfonate-based NHC are also summarized.*
*Please refer to dissertation for diagrams.
