Catalytic Platforms Using Aromatic Ions and Other Charged Species

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Project Summary. Chemical catalysis has long been a potent force for advancing biomedical research by enabling the construction of biologically important molecules with ever-increasing speed, efficiency, and versatility. One of the most potent driving forces for progress in the area of catalysis has been the discovery of new catalytic platforms and concepts. The proposed research program is broadly focused on advancing the area of catalysis through the development of novel catalytic platforms that utilize stable but electrically charged species as a key part of their molecular anatomy. In particular, we have employed aromatic ions such as cyclopropenium ion and cyclopentadienyl anion for the design of several highly effective catalyst platforms. For example, we introduced cyclopropenimines as a new class of strong, neutral superbase, and we have developed a number of chiral cyclopropenimines that have proven to be highly effective for enantioselective BrØnsted base catalyzed transformations. Moving forward, the major challenge in this area is to develop catalysts that are capable of engaging substrates of increasingly lower acidity while still maintaining control over stereoselectivity. Our continuing efforts are thus aimed at developing fundamentally new BrØnsted base platforms that will address this challenge. A second major application of aromatic ions that we have introduced is the pentacarboxycyclopentadienes (PCCPs) as a new platform for enantioselective BrØnsted acid catalysis. These catalysts are strongly acidic and are simple to prepare and to diversify, which stands in contrast to many of the established chiral BrØnsted acid platforms. In this area, the forefront challenge lies in learning how to generate and control the selectivity of increasingly unstabilized carbocation intermediates. Solving this challenge will require catalysts that are strongly acidic, chiral, and trivial to prepare, criteria which are very well satisfied by the PCCP platform. These and other investigations into the use of ionic structures to catalysis will continue to serve as a stimulus for advancements in chemical synthesis.