Synthesis of 2-Substituted 1,2-Dihydronaphthalenes and 1,2-Dihydroanthracenes Using a Recyclable Molybdenum Dearomatization Agent

Polycyclic aromatic hydrocarbons (PAHs; e.g., naphthalene and anthracene) form stable η²-bound complexes with the dearomatizing fragment {TpMo(NO)(MeIm)} (where Tp = hydridotris(pyrazolyl)borate; MeIm = 1-methylimidazole). These complexes undergo protonation at the α carbon followed by regioselective nucleophilic addition at the adjacent β carbon. The nucleophile (a pyrrole or an enolate) adds stereoselectively, anti to the face of metal coordination. The resulting 1,2-dihydroarene ligand may be isolated via metal oxidation by iodine to provide the free 1,2-dihydroarene in moderate yield (∼60%), as well as TpMo(NO)(MeIm)(I), the precursor of the original PAH complex (∼80–90%). Thus, a formal catalytic cycle for the dearomatization of naphthalene and anthracene has been demonstrated.