Selective anodic fluorination of phthalides in ionic liquids

Anodic fluorination of phthalide and its derivatives was carried out using Et4NF·4HF, Et3N·5HF and imidazolium ionic liquids like 1-ethyl-3-methylimidazolium triflate [emim][OTf]. Despite the high oxidation potential of phthalide, the fluorination proceeded efficiently in ionic liquids (ILs) containing fluoride salts. Fluorodesulfurization of 3-phenylthiophthalide took place predominantly in [emim][OTf] and CH2Cl2 while the use of 1,2-dimethoxyethane (DME) resulted in selective α-fluorination without the desulfurization. It was also demonstrated that the electrochemical fluorodesulfurization could be achieved by the reuse of IL. This is the first example of selective anodic fluorination using imidazolium ionic liquids.