1-Trifluoromethyl-1,2-benziodoxol-3-(1H)-one (1) is able to transfer the electrophilic CF3 group to the oxygen atom of THF in the presence of a Lewis or Bronsted acid. This results in a new ring-opening reaction of THF yielding trifluoromethyl ethers. Details of this reaction and the insight gained into the mechanism of action of reagent 1 are reported.