Fast Halogenation of Some N-Heterocycles by Means of N,N'-Dihalo-5,5-dimethylhydantoin

摘要

An instantaneous, selective and high-yielding halogenation process is reported. The method operates with imidazoles, pyrazoles, and indoles under benign reaction conditions. The developed process involves the use of N,N'-dihalo-5,5-dimethyl-hydantoins (halo = chlorine, bromine, iodine) as halogenation reagents that are activated by catalytic quantities of a strong Br0nsted acid. Moreover, the halogenation process is switchable to produce either the mono- or di-halogenated products. Issues related to the reaction mechanism are investigated and a proposal for a reaction mechanism is disclosed.