Re-investigation of the coupling reaction of 2-aryl-1,1-dibromo-3,3,3-trifluoropropenes. Preparation of perfluoroalkylated [3]cumulenes

The coupling reaction of perfluoroalkylated 2-aryl-1,1-dibromoalkenes using zinc and copper(I) bromide gave stereoisomeric mixtures of [3]cumulenes and [4]radialenes. The ratio of [3]cumulenes and [4]radialenes mainly depended upon the reaction temperature and the electronic character of the aryl group. When the coupling reaction was carried out at -40 degrees C, (E)- and (Z)-[3]cumulenes were obtained in good selectivity and only trace amounts of [4]radialenes were detected by a (FNMR)-F-19 analysis. On the other hand, a similar reaction at -60 degrees C afforded a considerable amount of [4]radialene isomers. When the cis-[3]cumulenes were heated at an appropriate temperature, selective isomerization to trans-[3]cumulenes occurred.