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 )2 C6 H3 ]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.