The reaction of sterically crowded cycloaliphatic thioketones with phenyl(t
rifluoromethyl)mercury and sodium iodide in boiling benzene yielded gem-dif
luorothiiranes in fair yields whereas in the case of aromatic thioketones g
em-difluoroalkenes were obtained. The formation of these products is ration
alized by an addition of difluorocarbene onto the C,S-double bond, followed
by the extrusion of sulfur.