Practical synthesis of polysubstituted unsymmetric 1,10-phenanthrolines by palladium catalyzed intramolecular oxidative cross coupling of C(sp2)–H and C(sp3)–H bonds of carboxamides

Abstract

1,10-Phenanthroline derivatives are among the most commonly used ligands for organic synthesis. A short sequence for the practical synthesis of polysubstituted unsymmetric 1,10-phenanthroline compounds was developed based on the palladium-catalyzed oxidative cross coupling reaction of C(sp²)–H/C(sp³)–H bonds of carboxamides. DMAP as a preferred ligand was crucial for the reaction to avoid β-hydride elimination, which may be controlled by the π–π stacking effect between the aryl group of the substrate and DMAP, demonstrated by primary mechanistic studies and X-ray data of the substrate-Pd-DMAP complex.