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. Co-2(CO)(8)/P[3,5-(CF3)(2)C6H3](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 beta-naphthol products.