Discovering catalytic strategies for transition metal-catalyzed reactions to construct topologically complex organic scaffolds

PROJECT SUMMARY The development of general methods for the construction of sp3-rich (i.e. highly three-dimensional) organic scaffolds is a longstanding challenge in organic synthesis. High sp3 character imparts beneficial biological activities and pharmacokinetic properties into organic molecules, but because of their complexity, such compounds are underrepresented in libraries for drug discovery relative to sp2-rich compounds. Transition metal catalysis has revolutionized the construction of sp2-rich organic scaffolds, producing an array of general transformations that allow for the facile synthesis of diverse libraries of compound analogues for developing novel small molecule therapeutics. To establish similarly versatile methods for synthesizing sp3-rich organic scaffolds from simple starting materials, innovations in catalysis are needed. The research proposed herein employs innovative ligand and catalyst design as a means to discover novel and general scaffold-building methodologies that can transform simple starting materials (i.e. alkenes, dienes, arenes) into functionally and structurally complex products. In one area, we are developing unconventional ligand platforms that occupy underpopulated regions of ligand space for Pd catalysis for the development of olefin carbofunctionalization reactions. We have found that ligands derived from urea, which occupy a region of small organic ligands that is inaccessible to phosphines and N-heterocyclic carbenes, effectively promote heteroannulation reactions of ambiphiles and dienes. In addition, phosphine ligands with unconventional steric profiles can exert ligand control over site-selectivity for heteroannulations with dienes. Future work in this area will focus on expanding on these findings to develop a unified synthetic approach to preparing diverse aliphatic heterocycles, as well as selective, multicomponent carbofunctionalization reactions of olefins. These methodological developments will be enabled by both rational ligand design and computationally-aided ligand discovery. In another area, we are establishing Cu-diamine complexes as general catalysts for oxidative, radical addition reactions. Central to our reaction design is coordinating Cu catalysts to the substrate, which promotes selective generation of reactive radical intermediates that can add to olefins and arenes. Using this approach, we have discovered an aerobic amino- oxygenation of internal alkenes that engages diverse aryl-substituted alkenes and operates under mild conditions. Designing ligands that enhance the oxidative potential of Cu and facilitate coordination to substrates will enable the discovery of new catalytic reactivity in oxidative, radical olefin addition reactions, and provides a framework for the development of highly enantioselective transformations. These reactions will enable the rapid construction of diverse functional motifs and cyclic scaffolds with excellent catalyst control over chemoselectivity and stereoselectivity. In total, the proposed research program will result in the development of versatile catalytic methods for the efficient preparation of functional molecules that are relevant for discovering compounds with therapeutic potential, and thus will have a significant impact on biomedical sciences and human health.