Synthesis of the first fluorinated cantharidin analogues

Fluorinated cantharidin analogues (4–7) have been synthesized for the first time. The key step in each synthesis is an exo-selective Diels–Alder reaction of furan with the appropriate fluorinated maleic anhydride. 17O NMR measurements of 5–7 and the corresponding non-fluorinated parent compounds were undertaken to show the influence of the fluorine substituent(s) on the electronic properties of the oxygen atoms.