Efficient methods for the incorporation of nitrogen functional groups into organic molecules are critical for the discovery, development and production of pharmaceuticals and related biologically active molecules. This proposal addresses the oxidative coupling of alkenes and nitrogen nucleophiles (amides, imides and carbamates), which represents a long-standing challenge in synthetic organic chemistry. Recent results in our lab have led to several important breakthroughs in this area. Efficient palladium-catalyzed methods have been developed for the intramolecular oxidative amination of alkenes with molecular oxygen (and, in some cases, ambient air) as the stoichiometric oxidant. Unlike early precedents of this chemistry, these reactions are compatible with the use of well-defined palladium catalysts coordinated by oxidatively stable ancillary ligands. The latter property creates the opportunity to pursue enantioselective catalytic methods. Separately, the first methods for intermolecular aerobic oxidative amination of alkenes were developed. This proposal outlines a comprehensive program to expand the scope and utility of aerobic oxidative amination reactions and to develop enantioselective methods for the synthesis of nitrogen-containing heterocycles. The first thorough mechanistic studies of this class of reactions will be undertaken in order to gain insights into the factors that promote efficient product formation and contribute to substrate- and catalyst-controlled stereoselectivity. The mechanistic work will utilize a number of complementary approaches, including gas-uptake kinetic methods, in-situ spectroscopic analysis of catalytic reactions, the use of suitably designed substrate probes and density functional theoretical calculations to illuminate fundamental features of the reaction pathway. Mechanistic insights provide the basis for our synthetic efforts to expand the scope of Pd-catalyzed aerobic oxidation reactions, including the development of new methods for oxidative difunctionalization of alkenes (aminooxygenation and aminoalkylation). Diversely functionalized and stereochemically defined substrates for these reactions will be accessed via the Ireland-Claisen rearrangement and via condensation of chiral allylic and homoallylic alcohols with isocyanates. Use of these substrates in the synthesis of target structures such as small pyrrolidine alkaloids and aminosugar derivatives will enable us to probe important issues related to the diastereoselectivity and functional group compatibility of these methods. New chiral palladium catalysts have been designed to pursue enantioselective catalysis. The goals in this area include the development of a completely new class of N-heterocyclic-carbene ligands based on a seven-membered heterocyclic framework that exhibits axial chirality. Insights from recent mechanistic studies suggest that chiral anionic ligands represent additional promising targets for the catalytic asymmetric synthesis of nitrogen heterocycles.
The development of efficient methods for the synthesis of organic molecules is critical for the discovery, development and commercial production of pharmaceuticals and therapeutic agents. The research outlined in this proposal will lead to new catalytic methods for the preparation of such biologically active molecules.
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|Zheng, Changwu; Stahl, Shannon S (2015) Regioselective aerobic oxidative Heck reactions with electronically unbiased alkenes: efficient access to ?-alkyl vinylarenes. Chem Commun (Camb) 51:12771-4|
|Weinstein, Adam B; Stahl, Shannon S (2014) Palladium Catalyzed Aryl C-H Amination with O2 via In Situ Formation of Peroxide-Based Oxidant(s) from Dioxane. Catal Sci Technol 4:4301-4307|
|Wang, Dian; Izawa, Yusuke; Stahl, Shannon S (2014) Pd-catalyzed aerobic oxidative coupling of arenes: evidence for transmetalation between two Pd(II)-aryl intermediates. J Am Chem Soc 136:9914-7|
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