Development of New Palladacycle Catalysts for the Asymmetric Reactions of Allylic Trichloroacetimidates

Chapter 1. This chapter provides a review of the evolution of palladacycles within the field of homogeneous catalysis. Their discovery, early uses as precatalysts for Pd(0)-promoted reactions, and contemporary uses in asymmetric catalysis are discussed. An in-depth discussion regarding approaches to the synthesis of palladacycles is also presented. Studies toward the development of planar-chiral palladacycles as asymmetric catalysts for the enantioselective formation of allylic carbon-heteroatom bonds is summarized, with a focus on work preformed in the Overman Group regarding enantioselective reactions of prochiral allylic trichloroacetimidates.;Chapter 2. Presented herein is the synthesis and evaluation of a library of novel homochiral palladacyclic imidazoline naphthalene (PIN) catalysts for the enantioselective reactions of prochiral allylic trichloroacetimidates. This new Pd(II) catalyst motif relies on steric interactions between the central naphthalene ring and imidazoline heterocycle to create a rigid and adjustable axial chiral environment around the metal center. Positioning of the chiral pocket can be adjusted by careful choice of the imidazoline substituents, proving a handle to optimize catalyst structure. Monomeric (S)-PIN-acac complexes were evaluated as catalysts for both the allylic imidate rearrangement and allylic esterification of (Z)-allylic trichloroacetimidates, exhibiting excellent catalytic activity in the latter reaction. Although this catalyst motif did not provide an advantage over extant planar-chiral cobalt oxazoline palladacycle (COP) catalysts, insight into the ideal positioning of the chiral environment around the Pd(II) center was garnered.;Chapter 3. Building from the conclusions discussed in Chapter 2, this chapter presents the synthesis and evaluation of a library 2-arylpyrrorlidine palladacycle (APP) catalysts, wherein the axial chiral pocket of the C,N-palladacycle has been created in closer proximity to the Pd(II) center. The APP motif displays excellent catalytic activity in the S N2'' displacement of (Z)-allylic trichloroacetimidates with acetate nucleophiles, affording chiral, non-racemic allylic acetates in high yield and moderate enantiomeric excess. The repositioning of the chiral environment is shown to increase enantioselectivity relative to the PIN catalyst motif. A summation of the important conclusions regarding the design of enantioselective palladacycle catalysts is presented.