Selectivity in the hydrogenation of 6- and 8-substituted-quinolines

Abstract

Quinoline (1) and the 6- or 8-substituted-quinolines (2)–(14)(R = Me, Prⁱ, Bu^t, Ph, OMe, OH, CF₃, or F) were hydrogenated catalytically on platinum under either weakly basic (solvent McOH) or strongly acidic (solvent CF₃CO₂H) conditions. In methanol the only product was the corresponding 1,2,3,4-tetrahydro-compound. In trifluoroacetic acid, compounds hydrogenated in the benzene ring were isolated as major products; both electronwithdrawing and electron-donating substituents at C-6 or C-8 cause (sometimes drastic) reduction in yield. The products were characterized by their ¹H and ¹³C n.m.r. spectra.