Investigation of mechanistic and synthetic aspects of organic photochemical reactions

The investigations described in this dissertation focus on (1) mechanistic studies of single electron transfer (SET) promoted photochemical reactions of polydonor-tethered naphthalimides, and (2) synthetic applications of pyridinium salt photochemistry. Studies in the first area involve efficient and regioselective SET-promoted macrocyclization reactions of polydonor-linked naphthalimides which are used to construct cyclic polyethers, polythioethers, polyamines, polysulfonamides and polypeptides. The synthetic importance of these macrocyclization reactions serves as the rational for detailed studies which I have carried out to determine how factors, such as donor oxidation potentials, rates of cation radical alpha-fragmentation reactions, and distances between donor and acceptor sites, govern both the chemical and quantum efficiencies and regioselectivities of these excited state processes. By using a combination of reaction chemical and quantum yield measurements along with fluorescence quantum yield determinations, I have demonstrated that the efficiencies of photomacrocyclization reactions of polydonor linked naphthalimides depend on the number, types, location and reactivity of ion radical centers formed by either direct or intrasite SET.; The second research problem described in this dissertation focuses on further developing the unique preparative potential of a new strategy for functionalized indolizidine synthesis. This strategy, which takes advantage of pyridinium salt photochemistry and ring rearrangement metathesis, has been used to design and execute concise syntheses of the polyhydroxylated indolizidine natural products (+)-castanospermine and possible uniflorine-A stereoisomers.; In the third section of this dissertation is described the results of an investigation probing the factors that govern the regiochemical course of photocyclization reactions of 1,2-cylcopenta-fused and 1,2-cyclohexa-fused pyridinium salts. In this effort, I found that irradiation of 1,2-cyclopenta-fused pyridinium perchlorate in an aqueous base solution results in efficient formation of a single tricyclic-allylic alcohol. This process and ensuing aziridine ring opening and enzymatic desymmetrization reactions are key components of novel routes I have developed for concise formal total syntheses of (-)-cephalotaxine. (Abstract shortened by UMI.)...