Book excerpt: Iron catalysts in organic synthesis are strongly in demand because iron is non-toxic, inexpensive and the most abundant transition metal in the earth, although their use is still limited compared with that of rare, precious metals such as palladium, ruthenium and rhodium. This thesis describes the first practical example of iron catalysis in the carbon–hydrogen bond activation reaction to synthesized fused aromatic ring compounds. By using a unique combination of iron catalyst and dichloride oxidant, various kind of naphthalene and phenanthrene derivatives were synthesized via annulation reaction with alkynes including direct C–H bond activation process. This achievement opens the new possibility of low-valent iron catalysis and expands synthetic methods for a sustainable society.