Stereoselective Isomerization of Tetrakistrifluoromethyl Tetraaryl [4]Radialenes to the Type II (All-Z) Isomers

Coupling reaction of 2-aryl-1,1-dibromo-3,3,3-trifluoropropenes using zinc and copper(I) bromide gave [4]radialenes in almost statistic ratios in addition to [3]cumulenes. Thermal dimerization of the cumulenes in neat gave mixtures of four isomeric [4]radialenes in moderate yields. When the isomers were heated in solid at appropriate temperatures, thermal isomerization occurred to afford type II (all-Z) isomers of [4]radialenes in high selectivity.