Cobalt-Catalyzed Intramolecular Alkyne/Benzocyclobutenone Coupling: C–C Bond Cleavage via a Tetrahedral Dicobalt Intermediate

A Co(0)-catalyzed intramolecular alkyne/benzocyclobutenone coupling through C–C cleavage of benzocyclobutenones is described. Co₂(CO)₈/P­[3,5-(CF₃)₂C₆H₃]₃ was discovered to be an effective metal/ligand combination, which exhibits complementary catalytic activity to the previously established rhodium catalyst. In particular, the C8-substituted substrates failed in the Rh system, but succeeded with the Co catalysis. Experimental and computational studies show that the initially formed tetrahedral dicobalt-alkyne complex undergoes C1–C2 activation via oxidative addition with Co(0), followed by migratory insertion and reductive elimination to give the β-naphthol products.