Applications of Oxoammonium Salts to Green Organic Reactions

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Supported by the Chemical Synthesis Program in the NSF Division of Chemistry, Professor Paul Floreancig at the University of Pittsburgh uses electrochemistry to the synthesize complex organic compounds. Electrochemical reactions use electrical currents in place of traditional chemicals. Chemical reagents often produce undesired by-products because they produce too much or too little energy to make (or break) specific chemical bonds; Because electrical currents can be precisely controlled at a given potential (voltage), electrochemical reactions can be tuned to provide just the right amount of energy needed for a desired transformation. In this way, electrochemical reactions promise to reduce chemical waste when compared to traditional chemical reactions. This research produces new environmentally benign synthetic methods using electrochemical techniques. The research team works with collaborators to combine organic reaction development with theory and electrochemical techniques. The new method development illustrate the power of employing oxidation reactions in increasing molecular complexity. The research team has a strong commitment to pursuing green chemistry and lessons learned through this research are used as examples in undergraduate classes directed toward environmentally benign organic synthesis. This project uses electrochemical oxidations to advance the oxidative carbon-hydrogen bond cleavage processes that have been developed in the Floreancig group. The study replaces quinone oxidants, which were originally used as stoichiometric reagents, with oxoammonium ions. The oxoammonium ions are more readily regenerated through anodic oxidation than their quinone counterparts and offer additional advantages, such as easier reactivity tuning and the potential for developing asymmetric variants for enantioselective synthesis. The first objective is to optimize the electrochemical regeneration of oxoammonium ions in oxidative cyclization reactions to allow for low catalyst loading by exploring the impact of oxidant strength, electrode material, and substrate oxidation potential. The second objective is to gain insight into the mechanistic nuances of oxidative carbon-hydrogen bond cleavage by oxoammonium ions through a combined experimental and theoretical approach that provides information on the importance of charge transfer and geometry of the transition states. The third objective is to develop new transformations that are possible with oxoammonium ions but not quinones, including cycloaddition reactions and kinetic resolutions. By disseminating the results through publication and seminars, the Floreancig group provides the scientific community with powerful new transformations, valuable mechanistic insights, and blueprints for interfacing electrochemistry with oxidative functionalization reactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.