Transition Metal-Catalyzed Enantioselective Silylation of C–H bonds: Reaction Development and Mechanistic Studies
The following dissertation discusses the development of catalytic enantioselective silylation of aryl, cyclopropyl and unactivated aliphatic C–H bonds. This work also includes in-depth studies that reveal the mechanism of the enantioselective silylation and the origin of enantioselectivity.
Chapter 1 reviews transition metal-catalyzed reactions that functionalize C–H bonds with an emphasis on enantioselective transformations. This review describes the representative strategies of C–H bond functionalization to obtain site-selectivity. Discussions on the development of enantioselective functionalizations of C–H bonds with representative examples follow.
Chapter 2 discusses the development of rhodium-catalyzed enantioselecitve silylation of aryl C–H bonds. Hydrosilyl ethers that are formed in situ by hydrosilylation of benzophenone or its derivatives undergo enantioselective C−H silylation in the presence of a rhodium catalyst. Enantioenriched benzoxasilole products from the silylation process undergo a range of transformations to form C−C, C−O, C−I, or C−Br bonds without erosion of enantiomeric excess.
Chapter 3 discusses experimental and theoretical studies on the mechanism of rhodium-catalyzed enantioselective silylation of aryl C−H bonds. The identity of the resting states of the catalyst, the kinetic data, and the results of DFT calculations provide detailed insights into the mechanism of intramolecular enantioselective silylation of aryl C−H bonds and the origin of enantioselectivity.
Chapter 4 discusses the development of rhodium-catalyzed enantioselecitve silylation of cyclopropyl C–H bonds. Hydrosilyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo enantioselective silylation of cyclopropyl C–H bonds in the presence of a rhodium catalyst. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao–Fleming oxidation to form cyclopropanols with conservation of the ee value from the C–H silylation.
Chapter 5 discusses the development of iridium-catalyzed silylation of unactivated sp3 C–H bonds of amines. The introduction of silylmethyl group on a secondary amine allows a site-selective functionalization of β-C–H bonds of amines to form silapyrrolidines. Development of both non-enantioselective and enantioselective catalysts is described. The silapyrrolidne product serves as a precursor to 1,2-amino alcohols by the oxidation of the silapyrrolidines, leading to an overall site-selective, and even enantioselective, oxidation of amines at the β-C–H bonds.