Aromatization of 2+2 cycloadducts of butadienes and fluoroolefins other than tetrafluoroethylene

Abstract

The 2+2 cycloadducts of fluorinated olefins other than tetrafluoroethylene and hydrocarbon dienes also ring-expand and eliminate two moles of hydrogen halide to form aromatic products. The hydrogen halide eliminated from chlorofluoroolefin adducts depends on the solid present during the aromatization. Alumina and other accelerators favor elimination of HF, while HCl evolves in the presence of inert solids such as SiC. The aromatics derived from hexafluoropropene adducts generally have the more sterically hindered regiochemistry. Alumina promotes extrusion of difluorocarbene from trifluoromethylcyclobutanes leading to fluorobenzenes rather than benzotrifluorides. Carbon accelerates these aromatizations without difluorocarbene extrusion.