Asymmetric Hydrogenation of Azaindoles: Chemo- and Enantioselective Reduction of Fused Aromatic Ring Systems Consisting of Two Heteroarenes.

High enantioselectivity was achieved for the hydrogenation of azaindoles by using the chiral catalyst, which was prepared from [Ru(η(3) -methallyl)2 (cod)] and a trans-chelating bis(phosphine) ligand (PhTRAP). The dearomative reaction exclusively occurred on the five-membered ring, thus giving the corresponding azaindolines with up to 97:3 enantiomer ratio.