Development of Binaphthyl-Based Chiral Ligands for Dirhodium(II) Complexes, Studies toward the Total Synthesis of Carnosol, and Allylic Substitution of Silylenol Ethers

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.