New radical iodoamide reagent conquers challenging iodoalkane synthesis

Alkyl halides are go-to starting reagents for synthetic organic chemists. Researchers tend to value iodoalkanes the most because they possess the weakest carbon-halogen bonds and are the most easily functionalized. Yet making alkyl iodides is thermodynamically unfavorable, and the reaction can inconveniently revert back to the starting materials, which means researchers often end up reaching for bromides, chlorides, or fluorides instead. A team has now developed a new N-iodoamide radical precursor capable of direct C–H bond iodination that seems to have overcome the challenge of easily making iodoalkanes (J. Org. Chem. 2017, DOI: 10.1021/acs.joc.7b00557). The achievement was made possible by combining the experience in C–H activation chemistry of Peter R. Schreiner’s group at Justus Liebig University and the experience in developing reactive nitrogen-centered molecules of Mark Gandelman’s group at Technion—Israel Institute of Technology. The researchers found via mechanistic and spectroscopic studies that light-activated iodo-3,5,5-trimethylhydantoin is the only compound so far that forms a nitrogen-centered radical capable of serving as a stable iodine donor for direct C–H iodinations. They show that the N-iodoamide reagent can be used to iodinate a range of linear and cyclic aliphatic C–H bonds. The reagent is also capable of iodinating benzylic C–H bonds, including carrying out the “missing” iodine version of the popular Wohl-Ziegler reaction.