POLYHALOAROMATICS .5. SYNTHESIS OF POLY-FLUORO-1,3,5,7-TETRAHYDROBENZO (1,2-C-4,5-C') DIFURANS AND PERFLUORO-1,3,5,7-TETRAHYDROBENZO[1,2-C-4,5-C']DIFURANS

Treatment of dichloro- or dibromopyromellitic acids 1 or 2 with a mixture of sulphur tetrafluoride and hydrogen fluoride gave the respective 4,8-dihalo-1,1,3,3,5,5,7,7-octafluoro-1,3,5,7-tetrahydrobenzo [1,2-c:4,5-c']difurans (3) and (4) in high yields. Dichloro compound 3 easily undergoes halogen-exchange with potassium fluoride to give perfluoro-1,3,5,7-tetrahydrobenzo[1,2-C:4,5-C'] difuran (5). Reduction of dibromocompound 4 with lithium aluminium hydride gave, depending on the reaction conditions, 1,1,3,3,5,5,7,7-octafluoro-1,3,5,7-tetrahydrobenzo[1,2-c:4,5-c']difuran (6) or 4-bromo-1,1,3,3,5,5,7,7-octafluoro-1,3,5,7-tetrahydrobenzo[1,2-c,4,5-c']difuran (7).