A Study of Polyene Systems: Reactivity of Siloxydienes and Dienolates

This thesis contributes a detailed analysis of the properties and reactivity of polarized polyene systems, particularly dienolates, and their neutral analogs, siloxydienes. These systems are notable for their distinctive electronic properties, including extended and polarized π-electron delocalization, which controls the site of reaction in these polyfunctional systems and facilitates remote functionalization reactions with an increased number of reaction centers. The primary focus of this work lies in the development and optimization of the iron-catalyzed oxidative dimerization reaction of siloxydienes. Under mild reaction conditions, a novel gamma-gamma (γ-γ) C–C bond is created. The reaction exhibits a broad substrate scope, encompassing cyclic and acyclic siloxydienes derived from ketones, aldehydes, and esters, leading to the formation of synthetically challenging 1,8-dicarbonyl compounds. Conceptually, the dienol ether serves as a precursor to a conjugated radical cation, which undergoes highly site-selective γ-dimerization reactions. The γ-γ dimerization strategy is applied to the synthesis of a bioactive analog of honokiol, demonstrating the utility of this method for complex molecule synthesis. Mechanistic investigations, including kinetics, Hammett plot analysis, cyclic voltammetry (CV), and Eyring and Arrhenius analyses, are undertaken to elucidate this transformation. As a side product in some cases, gamma-oxygenation reactivity is observed and optimized utilizing a catalytic iodine system. Furthermore, a general, regioselective, and metal-free γ-fluorination of α,β-unsaturated carbonyls via silyl dienol ethers is developed, providing access to valuable organofluorides. The regioselectivity of the reaction is found to be influenced by the conformational flexibility of the substrate. Diversification of the γ-fluorocarbonyls highlights the potential of fluorine as a stereocontrol element. In addition to methodological studies on siloxydienes, the utilization of dienolates in the total synthesis of resorcinol natural products is explored. This provides an alternative “non-aromatic” approach to this class of bioactive molecules, which exhibits advantageous opportunities for diversification within this framework.