Planar Chiral (η6-Arene) Ruthenium Cp Complexes in Organic Synthesis: Diastereoselective Complexation of Arene Compounds with Benzylic Alcohol and Its Synthetic Application to Chiral Biaryls

1- o -Substituted phenylethanols gave diastereoselective ruthenium Cp complexes via coordination of ruthenium with benzylic oxygen. This reaction can be further applied to the diastereoselective ruthenium complexation of δ-lactone-bridged biaryls possessing a chiral benzyl alcohol function at the side chain. Although δ-lactone-bridged biphenyls 10a and 10b exist as an inseparable equilibrated atropisomeric mixture, the corresponding ruthenium complexes 11a and 11b were obtained as a single compound, respectively, with differentiated arene face complexation and fixation of the central bond. Analogous biaryl compound 15 with a naphthalene fragment gave three Cp ruthenium complexes, 16, 17, and 18, in various ratios depending on reaction temperature. Naphthalene ring-coordinated ruthenium complex 16 was isomerized to the complex 17 via axial isomerization and ruthenium fragment migration to the inverted arene face by heating at 50 °C in dichloroethane, and the ruthenium complexes 16 and 17 were further transformed to benzene ring-coordinated ruthenium complex 18 by heating at 90 °C. The diastereoselective ruthenium complexation with fixation (and isomerization) of the axial bond of δ-lactone-bridged biaryls 10 and 15 was supported by ab initio calculations. Also, the ab initio calculations of δ-lactone-bridged biaryl ruthenium complexes with a naphthalene fragment were well consistent with the experimental results. The obtained ruthenium complexes of δ-lactone-bridged biaryls afforded axially chiral biaryls by ring opening of δ-lactone with nonchiral reagents.