Cascade iodination–fluorination synthesis of 2-fluorothiophene and 5-fluoro-2-thienyliodonium salts

The first synthesis of fluorine-containing 2-thienyliodonium salts was accomplished using cascade iodination–fluorination. According to this methodology, thiophene is first converted to bis(2-thienyl)iodonium hexafluorophosphate using an electrophilic iodination reaction. Upon heating with potassium fluoride, this salt undergoes regioselective fluorination producing 2-fluorothiophene. 2-Fluorothiophene is then iodinated again to yield fluorothienyliodonium salts.