Selective Halogen Migration Reactions at Mixed Halothiophenes

Preparation of starting compounds

Our intention was to study halogen-dance reactions at di-halogenated thiophenes. As starting products

2-bromo-3-chlorothiophene
3-bromo-2-iodothiophene
3-chloro-2-iodothiophene

have been chosen, as they provide a-halogens for specific transhalogenation.

2-Bromo-3-chlorothiophene was prepared via NBS bromination according to I.A. Barnish, P.E. Cross, R.P. Dickinson, M.J. Parry and M.J. Randall, J. Med. Chem. 1981, 24, 959:

3-Bromo-2-iodothiophene was prepared following S. Gronowitz and B. Holm, Acta Chem. Scand. 1976, B30, 423:

3-Chloro-2-iodothiophene was prepared via iodination with iodine/HIO₃ in acetic acid/carbontetrachloride:

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