Partially fluorinated heterocyclic compounds. Part 14. Syntheses of 4,5,6,7-tetrafluoro-2,3-dihydro-2-methyl-1-benzothiophen and 5,6,7,8-tetrafluorothiochroman from pentafluorophenyl prop-2-enyl sulphide via the Claisen rearrangement intermediate and the related reaction of prop-2-enyl 2,3,5,6-tetrafluorophenyl sulphide. Reactions which appear to proceed via homolytic fission of an aliphatic carbon–fluorine bond

Abstract

Prop-2-enyl 2,3,4,5-tetrafluorophenyl sulphide (1) undergoes a Claisen rearrangement in NN-diethylaniline to give 4,5,6,7-tetrafluoro-2,3-dihydro-2-methyl-1-benzothiophen (4) and 5,6,7,8-tetrafluorothiochroman (5). Pentafluorophenyl prop-2-enyl sulphide (3) in NN-diethylaniline also gave (4) and (5) accompanied by prop-2-enyl 3,4,5,6-tetrafluoro-2-(prop-2-enyl)phenyl sulphide (10), ethyl pentafluorophenyl sulphide (9), and perfluoropoly(phenylene sulphide). Prop-2-enyl 2,3,5,6-tetrafluorophenyl sulphide (2) reacted similarly to give 4,6,7-trifluoro-2,3-dihydro-2-methyl-1-benzothiophen (6), 5,7,8-trifluorothiochroman (7), ethyl 2,3,5,6-tetrafluorophenyl sulphide (8), and N-ethylaniline. Homolytic fission of the aliphatic C–F bond in the respective Claisen rearrangement intermediates from (3) and (2) is proposed to account for the formation of (4), (5), and (10), and of (6) and (7). Compounds (8)–(10) were synthesised by other methods.