Counter-ion Directed Enantioselective Approaches to Axially Chiral Materials

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Axial chirality is a term used to refer to stereoisomerism resulting from the non-planar arrangement of four groups in pairs around a chirality axis. Such compounds are exemplified by hindered biaryls, certain classes of spiro compounds, and allenes. Atropisomerism is a phenomenon whereby restricted rotation about a single bond leads to the formation of stereoisomers, and is a key feature of natural products, drug molecules and catalysts. It's increasing importance in all of these fields means that new methods for the enantioselective synthesis of atropisomeric compounds are extremely important. The aim of this proposal is to develop and exploit new catalytic enantioselective methods for the construction of axially chiral molecules. We propose that chiral ammonium counter-ions can be employed to control the stereochemistry of these reactions through kinetic resolution and dynamic kinetic resolution processes. We also propose a light-mediated racemization process that can be coupled with a counter-ion-mediated kinetic resolution, enabling the dynamic kinetic resolution of biaryls with large barriers to rotation at room temperature. Finally, we aim to use these reactions as exemplars to probe the kinetics and mechanism of enantioselective phase-transfer catalysis.