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Gold(I)-Mediated Nucleophilic Additions to Allenes: from Enantioselective Catalysis to Supramolecular Chemistry

  • Author(s): Wang, Zhan
  • Advisor(s): Toste, F D
  • et al.
Abstract

The ability of gold(I) complexes to activate carbon-carbon multiple bonds for the addition of nitrogen and oxygen nucleophiles has emerged as an attractive synthetic method in organic chemistry. While many transformations catalyzed by gold(I) have been reported in recent years, few studies provide insight into the mechanism of gold(I) mediated processes. The first half of this thesis will discuss the development of an enantioselective gold(I)-catalyzed hydroamination of allenes with hydroxylamine and hydrazine nucleophiles and mechanistic studies of this and related systems. The second half of this thesis will cover our efforts to incorporate gold(I) catalysts into supramolecular host-guest complexes and will highlight potential advantages of this novel approach to gold(I) reactions.

Chapter 1. In this chapter, we report a novel enantioselective method for formation of isoxazolidines, pyrazolidines and tetrahydrooxazine heterocycles catalyzed by dinuclear bisphosphine gold(I) complexes. Furthermore, we discuss our efforts toward the development of a dynamic kinetic resolution of chiral allenes via intermolecular asymmetric hydroamination.

Chapter 2. We perform detailed kinetic studies to elucidate the mechanism of two transformations: the gold(I)-catalyzed hydroamination of allenes with hydrazine nucleophiles and the intramolecular hydroamination of dienes in the presence of alcohol co-catalysts. While the hydroamination of allenes proceeds via an outer sphere ¥ð-acid mechanism, the related reaction with dienes likely proceeds via a Lewis-acid assisted-Br©ªnsted acid pathway.

Chapter 3. This chapter will focus on our efforts to incorporate catalytically active gold(I) complexes into tetrahedral supramolecular guest of the form Ga4L6. Using such a complex, we catalyze the intramolecular hydroalkoxylation of allenes. We demonstrate that encapsulation of gold(I) increases the rate of reaction relative to Me3PAuBr and also leads to improved catalyst lifetime.

Chapter 4. Herein we apply the supramolecular host-guest complex with gold(I) and Ga4L6 to tandem reactions with enzymes. The encapsulated complex performs as well, if not better than the ¡°free¡± gold(I) complex in chemoenzymatic processes with a variety of esterase and lipases. In some cases the free gold(I) cations significantly reduce the rate of enzyme catalysis while the encapsulated complex has no effect on enzyme activity.

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