Bioinspired Catalytic Metallofoldamers

ended

Inspired by mimicking the characteristics of terpenoid cyclase enzymes, the goal of this proposal is to design new types of catalysts containing electrophilic transition metal centers that could simultaneously fold and activate polyunsaturated substrates promoting non-inherent cyclization modes. Our goal is unprecedented, although it is rooted on fundamental organometallic chemistry, in particular, on the known activation of polyunsaturated substrates by highly electrophilic transition metals. These unconventional cyclizations cascades challenge the paradigm that the intrinsic reactivity of the substrate is the relevant factor in carbocation-initiated processes and would provide access to large carbocyclic skeletons such as those present in taxol and ophiobolin enantioselectively in a single step under catalytic conditions. Although the initial work will be carried out with gold catalysts, a major goal of this research is to develop other general-purpose efficient chiral electrophilic catalysts based on zinc. To attain our goal, we will study more simple catalysts to delineate the factors that control the folding of polyenynes and polyenes. Thus, we will prepare new series of C2-chiral catalysts in which the stereogenic elements are close to the reaction site. Related C2-chiral systems will be generated by supramolecular hydrogen-bond pairing. A similar chiral arrangement could also be achieved by an intramolecular chiral anion translocation from the metal to a distant hydrogen-bond donor site. In addition, we will explore larger systems based on structurally well-defined metallic clusters to generate highly electrophilic chiral reactive sites. The folding and activation of polyunsaturated substrates will be studied first with a series of catalytic prototypes based on digold or heterobimetallic complexes with N-heterocyclic carbenes, diphosphines, mixed ligands of these types, as well as resorcinarene-phosphonite cavitant ligands.