This paper focuses on the synthesis of new aromatic compounds by thermal, photochemical, or oxidative cleavage reaction of the corresponding precursors. The precursor-methods are useful for the derivatization of the non-soluble aromatic compounds. We have applied retro Diels-Alder reactions for the preparation of new π-expanded porphyrinoid compounds such as [14]tribenzotriphyrin(2.1.1), tetrabenzoporphycene, dodecasubstituted porphycene, tetraanthraporphyin, butadiyne-linked tetrabenzoporphyrin dimer, and so on. We have investigated the photocleavage synthesis of pentacenes from the corresponding α-diketone precursors. This photoreaction enabled us to prepare 1,4,8,11-tetrasubstituted pentacene. The synthesis of new pentacene derivatives with electron-withdrawing substituents at 6,13-positions by oxidative cleavage reaction will be also reported.