An iron-catalyzed decarbonylation initiated [2 + 2 + m] annulation of benzene-linked 1,n-enynes with aliphatic aldehydes has been developed. These divergent annulations allow the one-step and efficient synthesis of various fused- or spiro-polycyclic frameworks. Tertiary aldehydes undergo decarbonylation/β-C(sp³)–H cleavage to afford [2 + 2 + 2] cyclization products, whereas secondary aldehydes undergo decarbonylation/α-C(sp³)–H cleavage to generate [2 + 2 + 1] cyclization products.