N-phenylmaleimide or maleic anhydride; Wilkinson's catalyst in 1,2-dichloro-benzene C60CH2N(CH3)CH(COOC2H5) heated at reflux for 18 h in the presence of 30 equiv N-phenylmaleimide or maleic anhydride;

in 1,2-dichloro-benzene Retro-Prato reaction; Reflux;