MODIFICATION AND INCORPORATION OF C(sp3)-RICH FRAGMENTS WITH PHOTOREDOX CATALYSIS

Abstract

Chemical synthesis is central to numerous fields of scientific inquiry, providing the fundamental building blocks and tools for research in not only chemistry, but biology, physics, and medicine, among others. Consequently, the discovery and development of new synthetically useful reactions can have an outsized impact on numerous fields. Photoredox catalysis has transformed the field of organic synthesis over the last 15 years by enabling a plethora of new transformations that occur under mild photoirradiation conditions. Through the ability of excited-state photocatalysts to perform electron, atom, or energy transfer with simple organic molecules and transition metal catalysts, highly reactive open-shell intermediates can be generated and subsequently used in a broad range of reactions. Notably, the unique properties of radicals allow for their use in transformations similar to those observed in two-electron reactions or as participants in fundamental steps and reactions that have no analog in closed-shell reactivity. The work described herein employs radical intermediates as key components of reactions that would be challenging or impossible to accomplish with traditional closed-shell reactivity. Chapter 2 discusses a contrathermodynamic epimerization reaction able to generate thermodynamically less-stable cis-configured cyclic diols from their more stable trans counterparts using iterative HAT to interconvert between stereoisomers and a simple boronic acid additive to transiently invert the thermodynamic properties of the two isomers. In Chapter 3, a novel photoredox/nickel cocatalyzed annulation reaction sequence is described that uses two sequential radical couplings in the same reaction vessel to construct highly pharmaceutically-relevant semisaturated fused heterocyclic systems. Chapter 4 describes efforts towards the direct trifluoromethylation of aromatic N–H bonds using a merger of photoredox and copper catalysis to promote an otherwise highly-challenging reductive elimination step.