Radical Cyclization of O-pentafluorobenzoyloximes having a (cyclohexadiene)Fe(CO)3 moiety

In the presence of atmospheric oxygen, O-pentafluorobenzoyloximes having a (2,4-cyclohexadienyl)Fe(CO)(3) moiety at the alpha-position cyclize smoothly to give trans-fused [(4,5,6,7-eta)-3a,7a-dihydro-3H-indole]Fe(CO)(3) complexes. The cyclization proceeds via radical chain mechanism initiated by molecular oxygen, in which pentafluorobenzoyloxyl radical plays a role as a chain carrier. Thus obtained trans-fused dihydroindole iron complexes readily isomerize to the cis-fused isomers on acidic silica gel or under basic conditions. Such isomers are converted to 3a,7a-dihydroindole or indole derivatives by the oxidative removal of the Fe(CO)(3) group.