A general approach to polysubstituted pyrroles

Exposure of a range of 3-hydroxy-2-sulfonylamino-4-alkynes to excess iodine delivers good yields of a series of iodopyrroles. Unexpectedly, the hydroxyl-dihydropyrroles, which were assumed to be the first-formed intermediates, turn out to be stable entities which have been isolated for the first time.

A series of alkynyl sulfonamides have been smoothly converted into the corresponding iodopyrroles, useful as precursors to highly substituted derivatives. The intermediate hydroxydihydropyrroles, surprisingly, proved to be stable, isolable compounds.