Development of Binaphthyl-Based Chiral Ligands for Dirhodium(II) Complexes, Studies toward the Total Synthesis of Carnosol, and Allylic Substitution of Silylenol Ethers
Setthakarn, Krit 1987-
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This dissertation presents three major projects. The first is the development of binaphthyl-based chiral ligands for dirhodium(II) complexes and their applications to enantioselective hydrazone-initiated carbene/alkyne cascade reactions. The second is the study toward the total synthesis of the natural product carnosol, using Rh(II)-catalyzed carbene/alkyne cascade reactions. The third is Brønsted acid-catalyzed allylic functionalization of silylenol ethers with organotrifluoroborates via oxyallyl cations. The synthesis and reactivities of a new chiral dirhodium(II) complex using chiral binaphthyl ligands, Rh2(R-KC4N)2, will be discussed herein. The structure of the new chiral rhodium(II) complex was based on Rh2(esp)2 and confirmed by single crystal X-ray diffraction. Reactivity studies with hydrazone initiated carbene/alkyne cascade reactions showed that the new chiral rhodium(II) complex can replicate or exceed the reactivity of Rh2(esp)2 in terms of product yields. Additionally, a second generation of rhodium(II) complexes based on Rh2(R-KC4N)2 has been designed, and its synthesis has been attempted. The second project relies on the use of a carbene/alkyne cascade reaction to construct bridged tricyclic molecules. The attempted synthesis of the core structure of carnosol implemented this carbene/alkyne cascade reaction using two key intermediates, a hydrazone and a diazo ketone. The third project explores a new strategy for functionalization of α-hydroxy silylenol ethers using organotrifluoroborate salts via oxyallyl cations. The preliminary studies showed that this new strategy provides promising results with broadened nucleophile scopes.