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Studies in asymmetric catalysis: Supramolecular catalysis and borane-assisted hydrogenation
Metal-catalyzed catalytic asymmetric reactions have gained enormous attentions and the utilities of such reactions have facilitated natural products syntheses to afford highly bioactive molecules. While these reactions have provided reliable methodologies to transform basic reactants into product(s) with highly enantio- and regioselective manners, the incompatibility with a many functional groups and the associated need to employ protecting groups increases the number of synthetic steps required. Herein, a solution to such an issue has been proposed in catalytic asymmetric hydroboration of styrene derivatives where supramolecular catalysts developed by Takacs et al. were used to achieve highly regio- and stereoselective reaction on functionalized alkenes without the usage of protection chemistry. Moreover, the usefulness of the chemo- and site selective chemistry was demonstrated by applying this methodology to carry out a total synthesis of anti-fungal compounds with no protecting group manipulations. Organoborons have been identified as one of the most versatile and important class of molecules due to the facts that they can be transformed into many different useful functional groups including boronic acids which are widely used as a coupling partner for Suzuki-Miyaura coupling reaction. Thus, studies of catalytic asymmetric hydroboration have shown exponential growth over the past decade. Despite many successful advancements in catalytic asymmetric hydroboration of various substrates, not much attention has been paid to a formation of hydrogenation by-product which is a common observation from various research groups around the world. In this thesis, mechanism of hydrogenation by-product was investigated by both experimentally and computationally and a boron assisted hydrogenation mechanism is proposed to account for the hydrogenation by-product.
Toyama, Kazuya, "Studies in asymmetric catalysis: Supramolecular catalysis and borane-assisted hydrogenation" (2016). ETD collection for University of Nebraska - Lincoln. AAI10100533.