New strategies to synthesize complex pyridines and tetrahydropyridines using main group chemistry
Date
2021
Authors
Fricke, Patrick J., author
McNally, Andrew, advisor
Crans, Debbie, committee member
Chen, Eugene, committee member
Kipper, Matthew, committee member
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Abstract
Pyridine and piperidine are important molecular scaffolds in small molecule drug development in medicinal chemistry research. Because of their importance, methods to synthesize complex pyridines and piperidines are highly desirable. Chapter one discusses the importance of these scaffolds in the pharmaceutical industry along with the history of pyridine and piperidine synthesis and the challenges that still remain. Chapter two discusses the switching strategies for selective installation of phosphonium salts on polyazines. The methods include an acylation, base-mediate, phosphine mediate, and order-of-reagent addition strategies. Additionally, we demonstrate how these methods can be applied to medicinal chemistry research during structure-activity relationship studies by derivatizing the phosphonium salts. Chapter three presents a new strategy for selective pyridine alkylation at the 4-position of the pyridine ring. Using a triazine chloride activating group allows for 4-selective phosphonium ylide formation inside the pyridine ring. A Wittig olefination-rearomatization sequence with an aldehyde then furnishes the alkylated pyridine. This method offers an alternative strategy to conventionally used metal-catalyzed cross coupling and Minisci-type reactions. Chapter four describes a stepwise reduction method for the synthesis of dihydropyridine and tetrahydropyridine. Using N-Tf activation allows for a selective hydride reduction to the dihydropyridine, which can subsequently undergo hydrogenation to the tetrahydropyridine.
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Subject
phosphonium
piperidine
ylide
phosphorus
hydrogenation
pyridine