Partially fluorinated heterocyclic compounds. Part III. The preparation of 4,5,6,7-tetrafluorobenzo[b]furan

4,5,6,7-Tetrafluoro-2,3-dihydrobenzo[b]furan-3-one has been prepared by the cyclisation and decarboxylation of ethyl 6-ethoxycarbonyl-2,3,4,5-tetrafluorophenoxyacetate and by the reaction of 2,3,4,5-tetrafluorophenoxyacetic acid with butyl-lithium followed by carbonation. Reduction and dehydration of the benzo[b]furan-3-one gave 4,5,6,7-tetrafluorobenzo[b]furan. The attempted electrophilic cyclisation reactions of 2,3,4,5-tetrafluorophenoxy-acetic acid, -acetyl chloride, and -acetaldehyde diethyl acetal are reported.