Microwave-Assisted Fluorination of 2-Acylpyrroles: Synthesis of Fluorohymenidin

Treatment of mono- and nonbrominated 2-acylpyrroles with Selectfluor under microwave conditions leads to fluorination of the pyrrole ring in the 5-position. In particular, 2-trichloroacetylated pyrrole can be fluorinated. As an example, dihydrofluorohymenidin was synthesized and dehydrogenated to fluorohymenidin as the first fluorinated pyrrole-imidazole alkaloid. Introduction of the vinyl double bond was achieved by chlorination of the 2-aminoimidazole moiety, followed by dehydrochlorination at 100 degrees C in DMF.