Transfer Hydrogenation of N- and O-Containing Heterocycles Including Pyridines with H₃N–BH₃ Under the Catalysis of the Homogeneous Ruthenium Precatalyst

In this study, we report a transfer hydrogenation protocol that utilizes borane–ammonia (H3N–BH3) as the hydrogen source and a commercially available RuCl3·xH2O precatalyst for the selective aromatic reduction of quinolines, quinoxalines, pyridines, pyrazines, indoles, benzofurans, and furan derivatives to form the corresponding alicyclic heterocycles in good to excellent isolated yields. Applications of this straightforward protocol include the efficient preparation of useful key pharmaceutical intermediates, such as donepezil and flumequine, including a biologically active compound.