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Jose Roque

Development and Application of Bond Cleavage Strategies: Skeletal Editing of Cyclic Amines and Electronically-Controlled C–H Activation

Tue, Jan. 10, 2023, 3:30pm
Taylor Auditorium, Frick Chemistry Lab B02
Host: Robert Knowles

Modern drug discovery has benefited from advancements in chemical reaction development. For example, C–H functionalization reactions has transformed how synthetic chemists approach the retrosynthetic analysis of bioactive compounds. Despite recent advances, the development of siteselective reactions remains a grand challenge in metal-catalyzed C–H functionalization. Typical retrosynthetic analysis results in simplified fragments by the removal of functional groups on the periphery of molecules. As a result, forward syntheses and diversification of molecules have focused on peripheral modifications. Inspired by the concept of scaffold hopping, the first part of the presentation will detail an approach to access novel chemical space by focusing on making structural edits to the core framework of molecules. The second part of the presentation will center on addressing site-selectivity and the need for more active first-row transition metal catalysts, as the low activity and limited scope of known first-row transition metal catalysts severely limit their utility. Cobalt precatalysts supported by pyridine dicarbene pincers have been developed to selectively functionalize electronically distinct C–H bonds without relying on directing groups contrasting traditional approaches. For example, the meta-selective C(sp2 )–H borylation of fluoroarenes, a significant challenge due to the weak coordinating ability and the similar size of fluorine and hydrogen, has been demonstrated. Mechanistic studies on fluoroarene borylation established a kinetic preference for C–H bond activation at the meta position, while cobalt-aryl complexes resulting from ortho C–H activation are thermodynamically preferred. As a result of these mechanistic insights, the selectivity of a C–H borylation can be switched with a single catalyst by simply modifying the reaction conditions.