Asymmetric Hydrogenation of Tetrapyridine-Type N-Heteroarenes Using Phosphine-Free Ruthenium Diamine Catalysts

Chiral ruthenium-catalyzed enantioselective hydrogenation of tetrapyridine-type N-heteroarenes was firstly developed.The partial reduction of adjacent tetraheteroaromatic substrates proceeded smoothly in the presence of phosphine-free chiral cationic ruthenium diamine complexes,affording unprecedented high reactivity,enantioselecitivity and diastereoselectivity(up to 93%yield,>99%ee and 92:8 dr).The potential application of chiral tetradentate pyridine-amine products as chiral ligands has been demonstrated in the Cu-catalyzed asymmetric Friedel–Crafts alkylation reaction between indoles and nitroalkenes.