Synthesis and Chemistry of Highly Fluorinated Bicyclohexenone

Article abstract of DOI:10.1021/jo00284a022

A series of highly fluorinated bicyclo<2.2.0>-5-hexen-2-ones (3) and their hydrates (4) have been prepared in two steps from hexafluoro Dewar benzene (1).Photolysis of exo-3H-pentafluorobicyclo<2.2.0>-5-hexen-2-one (3d) at low pressure in the vapor phase gave 1H-pentafluorocyclopentadiene (8), but in solution the principal product was pentafluorophenol (9).Under Favorskii conditions, exo-3-bromo- and exo-3-chloropentafluorobicyclo<2.2.0>-5-hexen-2-one (3a and 3b) ring opened stereospecifically to 2-cyclobutenecarboxylic acids 17 and 29, respectively.Treatment of these ketones with tert-butoxide under aprotic conditions effected stereospecific cleavage to tert-butyl methylenecyclobutenecarboxylates 25 and 30.The acid (27) corresponding to 25 was obtained both from bromohydrate 4a and the acid 17, again stereospecifically, by reaction with lithium diisopropylamide.Flash vacuum pyrolysis of the hydrate (4c) of of hexafluorobicyclo<2.2.0>-5-hexen-2-one at 300 deg C gave hexafluoro-2,4-cyclohexadienone (12), which decarbonylated at higher temperatures to yield hexafluorocyclopentadiene (13).Similarly, flash vacuum pyrolysis of 3-chloropentafluorobicyclo<2.2.0>-5-hexen-2-one (3b) at 650 deg C gave a mixture of 1- and 2-chloropentafluorocyclopentadienes.