Synthetic applications and mechanistic studies of cerium(IV) mediated reactions

Reagents based on Ce(IV) represent some of the most commonly utilized oxidants in organic synthesis. The chemistry of Ce(IV) oxidants is dominated by radical or radical cation intermediates with unstable and unpredictable properties that lead to side reactions. As a result, side-products are prevalent in many Ce(IV) mediated organic transformations and the application of Ce(IV) in organic chemistry has been limited. In this dissertation, new organic reactions or synthetic methodologies that employ Ce(IV) oxidants have been developed to broaden the utility of these reagents. Detailed mechanistic studies of Ce(IV) initiated reactions were carried out to provide the information necessary to fine tune reactions through controlled pathways thus leading to product selectivity.; Two Ce(IV) mediated solvent-dependent chemoselective oxidations of beta-dicarbonyl compounds have been developed. These reactions provide alternative synthetic methodologies for the preparation of carboxylic acids, beta-tetralones, alpha-tetralones, and dihydrofurans. To better understand the mechanism, the influence of solvent, Ce(IV) ligands, and substrate structure on the oxidation of beta-dicarbonyl compounds has been investigated. The stabilities and reactivities of radical cation intermediates in different solvents have also been analyzed based on kinetic and thermodynamic studies using stopped-flow spectrophotometry. Initial synthetic studies have been carried out on the coupling reaction of 1,3-dicarbonyls with isopropenyl acetate and the ring opening of cyclopropanols with inorganic anions in the presence of CAN. The former reaction generates 2-substituted 1,4-diketones in good yields and the latter offers a novel approach to beta-functionalized ketones via a carbon-heteroatom bond forming reaction.