In complex organic molecules, there are often many sites of equal reactivity. In the specific case of natural products and pharmaceuticals, our inability to perform reactions with positional selectivity limits the types of chemical modifications that can be made to a structure without needing to synthesize the desired targets from scratch. Weare developing new catalysts that can direct important reactions in a predictable way between (i) multiple nucleophilic sites, (ii) multiple electrophilic sites, or (iii) multiple benzylic C-H bonds.
ION PAIRED CATALYSTS
Simultaneous activation of two reaction partners by two independent catalysts offers new opportunities for reaction discovery. While numerous successes have already been demonstrated, this approach inherently faces two challenges: first, catalytic intermediates are present in low concentration, and the encounter of two of these species in solution may be kinetically limiting. Second, when using two chiral catalysts, control of their diastereomeric interaction may be difficult. We are developing ion paired catalysts to provide an increased rate of encounter in solution and an additional handle for adjusting their spatial interaction.
Electric fields that have been created by physical means such as parallel plate electrodes or ion-exchanged zeolites have demonstrated the ability to change the outcome of catalytic reactions. We modify well established asymmetric platforms with ionic groups to generate molecular zwitterionic catalysts in an effort to control stereo-, regio- and/or chemoselectivity in a way that is not offered by the parent catalyst.