Aromatic compounds with iodine substituents are useful intermediates in organic synthesis. They can be prepared using electrophilic aromatic substitution reactions. However, this reaction can be hampered by a lack of regioselectivity. In addition, the substrate scope can be limited: When common iodinating reagents such as N-iodosuccinimide (NIS) are used, electron-deficient arenes and heterocycles can be difficult to convert.

Tobias Ritter, Max Planck Institute for Coal Research, Mülheim an der Ruhr, and RWTH Aachen University, both Germany, and colleagues have developed a regioselective (hetero)arene C–H iodination reaction with an improved substrate scope. The team used a combination of molecular iodine and silver mesylate. They propose that a sulfonyl hypoiodite (MeSO₂–O–I) is formed from these compounds and then acts as a iodination reagent for different (hetero)arenes.

The desired iodinated products were obtained in mostly high to excellent yields. The reaction is selective and has a broad substrate scope and good functional group tolerance. With this protocol, electron-poor arenes can be iodinated—in contrast to approaches that use NIS as a reagent. The team also performed the reaction successfully on a gram scale.

• Selective C–H Iodination of (Hetero)arenes,
  Lalita Tanwar, Jonas Börgel, Johannes Lehmann, Tobias Ritter,
  Org. Lett. 2021.
  https://doi.org/10.1021/acs.orglett.1c01530