Addition of dihalocarbenes to vinyl fluorides. Chemical consequences of fluorine substitution. Part 3

1-Fluoro-1-phenylethene ( 1a ) or 1-(4-chlorophenyl)-1-fluoroethene ( 1b ) and 2-fluorooct-1-ene ( 4 ), on reaction with chloroform and sodium hydroxide, in a two-phase system in the presence of a phase transfer catalyst, gave the corresponding dichlorocyclopropanes in good yields. In a competition experiment, 1a was shown to be slightly more reactive than styrene itself. AM1 calculations predict reasonable activation barriers for these reactions although the relative reactivity observed in the experiment is not reproduced. For the ( E )- and ( Z )-1-fluoro-2-phenylethenes ( 3 ), higher activation barriers were calculated, in agreement with the observation that these alkenes did not react with dichlorocarbene under these conditions. The dibromocarbene addition to 1a gave 1,1-dibromo-2-fluoro-2-phenylcyclopropane ( 8 ), which on heating with silver salts in acetic acid yielded 3-acetoxy- 2-bromo-1-fluoro-1-phenylprop-1-ene ( 9 ) by a cyclopropyl-allyl rearrangement.