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 delta-lactone-bridged biaryls possessing a chiral benzyl alcohol function at the side chain. Although delta-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 degreesC in dichloroethane, and the ruthenium complexes 16 and 17 were further transformed to benzene ring-coordinated ruthenium complex 18 by heating at 90degreesC. The diastereoselective ruthenium complexation with fixation (and isomerization) of the axial bond of d-lactone-bridged biaryls 10 and 15 was supported by ab initio calculations. Also, the ab initio calculations of d-lactone-bridged biaryl ruthenium complexes with a naphthalene fragment were well consistent with the experimental results. The obtained ruthenium complexes of d-lactone-bridged biaryls afforded axially chiral biaryls by ring opening of delta-lactone with nonchiral reagents.