Thermal and photochemical isomerization of tetraaryl tetrakis(trifluoromethyl)[4]radialenes

isomerization of tetraaryl tetrakis(trifluoromethyl) [4]radialenes was studied. When type II (all-Z) isomers of 5,6,7,8-tetraaryl-5,6,7,8-tetrakis(trifluromethyl)[4]radialenes were heated in tetralin at 170-200 degrees C, isomerization occurred to give mixtures of four [4]radialenes in a ratio of ca. I:II:III:IV = 1:10:5:1. However, when the isomeric mixtures were heated in the solid state-at the same temperature, selective isomerization took place to give type II isomers in good selectivity (>91%). Upon irradiation with light, the type II isomers first isomerized to mixtures of the four [4]radialene isomers (I:II:III:IV = 2:2:48:48) and then rearranged to cyclobuta[b]naphthalenes via a 6 pi-electrocyclic reaction followed by 1,3-hydrogen migration.