POLYFLUORINATED HETEROCYCLIC-COMPOUNDS .29. THE SYNTHESIS OF 4,5,6,7,8-PENTAFLUORO-2H-CYCLOHEPTA[B]FURAN-2-ONE AND ITS REACTION WITH SODIUM METHOXIDE

Pentafluorophenyl propynoate (8), prepared from sodium pentafluorophenate and propynoyl chloride, on flash vacuum pyrolysis through silica gave 4,5,6,7,8-pentafluoro-2H-cyclohepta[b]furan-2-one (9). Treatment of (9) with sodium methoxide in methanol at -70-degrees-C produced a mixture of the 4-methoxy-, 5-methoxy-, 6-methoxy-, 7-methoxy- and 8-methoxy-tetrafluoro-2H-cyclohepta[b]furan-2-one compounds (10), (11), (12), (13) and (14) in the ratio 11:18:8:19:44 respectively. Under more forcing conditions, the 4,8- and 5,8-dimethoxy-trifluoro-2H-cyclohepta[b]furan-2-one compounds (15) and (16) respectively were formed. X-ray crystallography identified the 8-methoxy derivative (14), whose fluorine nmr spectrum enabled key resonances to be identified in the parent (9) and subsequently allowed the structures of all the other products to be deduced.