UC Berkeley

Enantioselective Carbon-Carbon Bond Forming Reactions and Photochemistry Enabled by High-Valent Gold Catalysts

Chapter 1 – A brief introduction to enantioselective gold catalysis is presented in this chapter. The limitations of enantioselective gold catalysis and the various methods that have been exploited to overcome these barriers in gold-catalyzed reactions are discussed. The potential of gold(III) as a solution to problems associated with enantioselective gold(I) catalysis is also proposed.

Chapter 2 – The direct enantioconvergent 1,5-enyne cycloisomerization and kinetic resolution catalyzed by a gold(III) complex is described in this chapter. This represents the first highly enantioselective transformation catalyzed by a well-defined cationic gold(III) species and further corroborates our hypothesis that gold(III) can be used to induce chirality in situations where gold(I) is not successful. The transformation produces highly enantioenriched bicyclo[3.1.0]hexenes at all levels of conversion while simultaneously resulting in enantioenriched 1,5-enynes. Additionally, the nature of the direct enantioconvergent kinetic resolution is further explored along with the substrate scope of the transformation.

Chapter 3 – A highly enantioselective Mukaiyama-Michael addition controlled by chiral phosphoramidite gold(III) catalysts is described in this chapter. To the best of our knowledge, this is the first report of a highly enantioselective Mukaiyama-Michael addition wherein silyl ketene acetals are suitable nucleophiles for the transformation, as well as the first report exploiting chiral phosphoramidite gold(III) catalysts as the source of chirality. The transformation was optimal with TADDOL-based phosphoramidite ligands on gold(III), resulting in high regio- and enantioselectivity. Additional studies are underway with prochiral silylketene acetals to also explore potential control of diastereoselectivity.

Chapter 4 – The photophysical properties of several gold(III) complexes and their use as dual Lewis acid-photocatalysts are described in this chapter. With triplet state energies in excess of 50 kcal/mol, the gold(III) complexes have been successfully used as photosensitizers for the generation of singlet oxygen used for the oxidation of benzylic amines. Preliminary results are promising for the development of a chemoselective oxidation of amines with potential use as a late stage functionalization technique.