Much Ado About Radicals: Mechanistic Studies in Photochemistry and SRN1 Reactions

Abstract

The second decade of the 21st century has witnessed a resurgence in the use of radical chemistry in both methodology and total synthesis. Many contemporary advancements can be attributed to the popularization of radical generation via photoredox catalysis, which negates the last few decades’ frequent use of stoichiometric or hazardous reagents in radical reactions. With these new techniques comes advanced understanding of the underlying radical redox mechanisms as well as new and unique questions. Due to the complexity inherent in the design of successful radical reactions, it is imperative to develop thorough mechanistic understanding. Herein our group has elucidated the mechanistic behavior of three distinct radical systems. The synthesis of a variety of phenanthridines and amides has been completed via radical addition to isonitriles catalyzed by the dimeric gold photocatalyst [Au2(dppm)2]Cl2. This catalyst has further enabled radical clock studies and has been used to determine the rate constant of primary radical addition to biphenyl isonitriles. The photoredox generation of chlorine atoms for HAT has been undertaken with the iridium polypyridyl complex [Ir(dF(CF3)ppy)2(dtbbpy)]Cl, with results supporting a tuning of HAT selectivity by solvent-chlorine complexation. Finally, mechanistic data suggest that single electron transfer from a base in DMSO catalyzes an unorthodox etherification of phenols.