Radical Cation/Anion and Neutral Radicals: A Comparison

Abstract

This article examines similarities between radical and radical ion reactions. Radicals and radical ions have worked there way into almost every facet of mainstream chemistry over the past 60 years. The importance as well as usefulness now associated with the reactions of radicals is in stark contrast to their prior role as poorly understood scapegoat molecules often blamed for failed reactions. The processes discussed herein demonstrate two critically important concepts to the radical chemist: (i) kinetic studies are an excellent and versatility applicable tool to determine mechanistic data for chemical reactions and (ii) published mechanistic data for more thoroughly studied radical processes have provided and continue to provide key insight into the factors governing reactivity and mechanism of their charge bearing counterparts.

Photochemical Regioselective C(sp3)–H Amination of Amides Using N-Haloimides

“…Heteroaromatic amides were also aminated in moderate yields ( 3bu and 3bv ). Importantly, unlike in previously reported aminations using 1b , our approach did not seem to lead to significant reaction with the aromatic moieties of the amides, and only small amounts of aminated chlorobenzene were observed. Finally, as expected, sulfonamides tolerated the reaction conditions well, furnishing desired product 3bw in 56% yield (Figure ).…”

“…This is similar to previously published transformations, indicating the formation of the imidyl radical. We presume that homolytic cleavage of the N- haloimide prior to activation by LiO t Bu is in part responsible for this side reactivity, which is observed as the primary product ( 7 ) in the absence of LiO t Bu. Also as previously mentioned in the table of optimization, in the absence of LiO t Bu or light no product is generated, and replacing N- haloimides with the nonhalogenated imide (such as phthalimide) does not generate any observable product (Scheme B).…”

“…The results show that the formation of an electron donor–acceptor (EDA) complex presents an exergonic energy profile (−14.6 kcal/mol), denoting that its formation is favored. Additionally, we also calculated two possible mechanistic pathways for the C–H activation step: (i) a hydrogen atom transfer (HAT) step between •O t Bu and the amide and (ii) an electron transfer/proton transfer (ET/PT) step . Exploration of both mechanistic pathways reveals that the reaction seems to follow a classic HAT mechanism.…”

“…Additionally, we also calculated two possible mechanistic pathways for the C−H activation step: (i) a hydrogen atom transfer (HAT) step between •OtBu and the amide and (ii) an electron transfer/proton transfer (ET/PT) step. 8 Exploration of both mechanistic pathways reveals that the reaction seems to follow a classic HAT mechanism.…”