Fluoro-olefin chemistry. Part IX. Thermal insertion of hexafluoropropene into carbon–hydrogen bonds in alkylbenzenes

Abstract

The thermal reactions (ca. 250 °C) of the alkylbenzenes ArCH₂R (Ar = Ph, R = H, Me, or Et; Ar =p-ClC₆H₄, R = H; Ar =p-MeC₆H₄, R = H) with hexafluoropropene give mainly the 1 : 1 adducts ArCHR·CF₂·CHF·CF₃, together with smaller amounts of the 1 : 1 adducts ArCHR·CF(CF₃)·CHF₂, 1-alkyl-2,2,3-trifluoro-3-trifluoromethylindanes, 1-alkyl-2,3,3-trifluoro-2-trifluoromethylindanes, and minor amounts of other products. Reaction at high pressure (autoclaves) favours 1 : 1 adduct formation whereas at lower pressure (tubes) indane formation is favoured. The reaction with cumene does not afford 1 : 1 adducts, the major products being 1,2,2,2-tetrafluoroethylbenzene, 1,1-difluoro-2-methylpropene, and the cyclobutane, [graphic omitted]F₂; indanes are also formed in this reaction. Chlorination, bromination, and nitration of the 1 : 1 adduct PhCH₂·CF₂·CHF·CF₃ gives the corresponding ortho- and para-substituted derivatives in the ratios 47 : 53, 20 : 80, and 0 : 100, respectively.