11:00am - 12:00pm
An important advance in organic chemistry has been the exploitation of aromatic ions as design elements to facilitate access to charged intermediates, and the Lambert group has made several contributions to this strategy. I will outline two such developments that feature cyclopropenium ions as the basis for their outcomes.
First, I will describe an alternative to a version of the Mitsunobu reaction catalyzed by cyclopropenones. As the direct nucleophilic substitution of alcohols is not typically possible, the Mitsunobu reaction has become the most widely used approach to this transformation in spite of its poor atom economy and purification challenges. In contrast, cyclopropenones enable a catalytic substitution of alcohols with sulfonic acid nucleophiles, wherein the sulfonic anhydride and amine reagents give water-soluble byproducts and the cyclopropenone catalyst is readily converted to a water-soluble derivative to simplify purification.
Next, I will detail the evolution of the recently discovered cyclopropenimine class of organic superbases into components of higher-order superbases. Such higher-order molecules offer much greater basicities than their parent superbases as well as tremendous promise as catalysts, but very few of their possible permutations have been reported. Therefore, robust methods for the preparation of six new classes of higher-order superbases have been developed. The first systematic analysis of their properties including basicity, molecular structures, stability, selectivity, and catalytic activity was also conducted.