Transition metal catalyzed C-C bond formation via transfer hydrogenation : from methodology development to polycyclic aromatic hydrocarbon syntheses
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Since the Nobel prize-winning discovery of the Diels-Alder reaction in 1928, cycloaddition reactions—chemical transformations to construct ubiquitous cyclic organic molecules—are one of the most important chemical reactions found in physical, biological, and organic chemistry. Despite their long history, cycloaddition reactions only proceed with a limited combination of π-unsaturated compounds, imposing severe limitations on their scope and applications in organic synthesis. By exploiting transition metal catalyzed transfer hydrognenation reactions and C-C formation, I disclosed a series of novel cycloaddition reactions starting from diols, an abundant and inexpensive compounds easily obtained from biomass. Because of the expediency with which diols can be accessed or their status as feedstock materials, these reactions represent a paradigmatic shift in the synthetic efficiency of cycloaddition reactions for building complex ring systems. Furthermore, those new methodologies were applied to a different and emerging field for our group: material science. Polycyclic aromatic hydrocarbons (PAHs) consist of conjugated aromatic rings and have attracted the attention of material scientists for their excellent electronic properties. Presently, over 3 million PAHs have been reported and synthesized. As the structural complexity of PAHs has greatly increased over the past two decades, the methodologies capable of accessing PAHs has remained stagnant following the introduction of the cross coupling reaction. By taking advantage of the newly developed cycloaddition methodologies, PAHs that are synthetically difficult or impossible with conventional methodologies could be realized. Our new cycloaddition methodology followed by simple dehydration yields PAHs using inexpensive and chemically stable diols. Moreover, our new methodology is highly functional group tolerant, including towards halides, allowing complimentary cross coupling methods to further functionalize the products. The hybridization of old and new technologies could derivatize well-known PAHs to novel structures with unusual symmetry and highly conjugated π-system. Consequently, I achieved the syntheses of hexabenzocoronene (HBC) with a new symmetry, S-doped helicene including picene moiety, and novel all-aromatic helical cages. Therefore, new methodologies for PAH construction that compliment current strategies will dramatically extend the types of materials that can be synthesized, including challenges unmet in material science.