Cationoid rearrangements in reactions of perfluoro-1-arylbenzocyclobutenes with antimony pentafluoride

Abstract

In the presence of antimony pentafluoride at 130 °C, the four-membered ring of perfluoro-1-(2-ethylphenyl)benzocyclobutene ( 2) undergoes cleavage, forming perfluoro-2-ethyl-2′-methyldiphenylmethane ( 5). Compound 5 is converted, under the action of SbF 5 at 170 °C, to perfluoro-8,9-dimethyl-1,2,3,4-tetrahydrofluorene ( 8). Perfluoro-1-(4-ethylphenyl)benzocyclobutene ( 3) remains unchanged at 130 °C, whereas at 170 °C it gives a mixture of perfluorinated 4′-ethyl-2-methyldiphenylmethane ( 9), 6-ethyl-1,2,3,4-tetrahydroanthracene ( 11) and 2-ethyl-9,10-dihydroanthracene ( 12). When heated with SbF 5 at 170 °C, perfluoro-1-phenylbenzocyclobutene ( 1) remains unchanged. Solution of compounds 2, 3, 5 and 9 in SbF 5–SO 2ClF generated the perfluorinated 1-(2-ethylphenyl)-1-benzocyclobutenyl ( 29), 1-(4-ethylphenyl)-1-benzocyclobutenyl ( 30), 2-ethyl-2′-methyldiphenylmethyl ( 31) and 4′-ethyl-2-methyldiphenylmethyl ( 32) cations, respectively.