Synthesis of Chiral Organofluorines via Catalytic Asymmetric C-C Bond Formation w

Georgetown University, Washington DC

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Abstract

DESCRIPTION (provided by applicant): Synthesis of Chiral Organofluorines via Catalytic Asymmetric C-C Bond Formation with Fluoroenolates, Alkynes and Ynamides The ever-increasing demand for chiral compounds and the rapid rise of fluoroorganic pharmaceuticals call for the development of new synthetic methods that provide practical access to a wide variety of fluorinated chiral building blocks. The introduction of new strategies that allow control of the unique stability and reactivity patterns of fluorinated nucleophiles and electrophiles offers invaluable opportunities to streamline chemical syntheses of current and future fluoroorganic drugs. We will develop a method for asymmetric catalysis with fluorinated nucleophiles generated in-situ and under mild conditions from readily available trifluoroacetyl derived precursors. The feasibility and practicality of this approach are demonstrated with ample preliminary results obtained by a copper-bisoxazoline catalyzed reaction using aliphatic and aromatic aldehydes. Continued ligand development and the planned mechanistic investigations will further improve the enantioselectivity of this reaction and extend this methodology to a range of currently elusive fluorinated nucleophiles. Using bisoxazolidine ligands recently developed in our laboratories we have found an entry towards a practical catalytic asymmetric alkynylation of trifluoromethyl ketones. Further ligand and method development will go hand-in-hand with mechanistic studies and screening of promising reaction parameters. We have made substantial progress with this important reaction and this experience provides a unique opportunity to introduce ynamides and ynesulfonamides to catalytic C-C bond formation. Our preliminary investigations provide promising proof-of-concept results obtained with a tosylated ynamide and show that this research direction will provide unprecedented access to a diverse range of new versatile chiral building blocks. The planned catalyst and reaction developments will be guided by detailed mechanistic studies and lead to in-depth investigations of the scope and applications of the proposed methods. Our multifaceted efforts will introduce in-situ generated fluoroenolates to asymmetric catalysis (Aim 1), a practical method for the alkynylation of trifluoromethyl ketones (Aim 2), and catalytic enantioselective addition reactions with ynamides and derivatives thereof (Aim 3). Additional emphasis will be given to the synthetic use and reactions of the new building blocks that will be generated by the wide range of electrophiles and nucleophilic species made available during this work.