Cobalt(I)‐Catalyzed Diels–Alder Sequences Involving Alkynes and Dendralenes

Abstract Dendralenes, the archetypal cross‐conjugated hydrocarbons, are shown to behave as multi‐diene systems in Co(I)‐catalyzed stepwise (4 + 2) cycloadditions with multiple C≡C dienophiles. The synthetic potential of [5]‐ and [6]dendralenes is unveiled for the first time, with high chemoselectivity, site‐selectivity, and orientational control — the latter demonstrated to be both catalyst‐directed and switchable. Formal (4 + 2) cycloaddition sequences, followed by pericyclic [4 + 2] cycloadditions and in situ oxidative aromatization, give rise to structurally diverse polycyclic aromatic hydrocarbons. The first heteroatom‐free Nazarov cyclization furnishes complex polycyclic scaffolds reminiscent of natural products. Finally, the use of dendralenes and cyclohexa‐1,4‐dienes is shown to extend the scope of macrocyclic hydrocarbon synthesis.