Remarkable Switch in the Regiochemistry of the Iodination of Anilines by N-Iodosuccinimide: Synthesis of 1,2-Dichloro-3,4-diiodobenzene

Direct iodination of anilines by NIS in polar solvents (such as DMSO) affords p-iodinated products with up to >99% ­regioselectivity. Switching to less polar solvents (such as benzene) in the presence of AcOH inverts this outcome toward dramatically increased or preferential generation of the o-isomers, also with up to >99% regioselectivity. This finding was exploited in the synthesis of 1,2-dichloro-3,4-diiodobenzene.