Facile synthesis of substituted phenanthroline ligands by samarium-promoted coupling of phenanthroline with ketones

[formula: see text] 1,10-Phenanthroline undergoes coupling with ketones promoted by samarium diiodide to produce 2-(1-hydroxyalkyl)-1,10-phenanthrolines. O-Methylation of these derivatives provides the corresponding 2-(1-methoxyalkyl)phenanthrolines. Demethoxylation with samarium diiodide then affords 2-alkylphenanthrolines. This process may be repeated to obtain 2,9-disubstituted phenanthrolines. A variety of new, substituted phenanthrolines are thus obtained. These compounds have numerous potential applications as ligands in metal-promoted reactions, including asymmetric catalysis.