Enantioselective Hydrogenation of 2-Methylquinoxaline to (−)-(2S)-2-Methyl-1,2,3,4-tetrahydroquinoxaline by Iridium Catalysis

The orthometalated dihydride complex fac-exo -( R )-[IrH 2 {C 6 H 4 C*H(Me)N(CH 2 CH 2 PPh 2 ) 2 }] is an effective catalyst precursor for the enantioselective hydrogenation of 2-methylquinoxaline (MeQ) to 2-methyl-1,2,3,4-tetrahydroquinoxaline (MeTHQ) with ee's up to 90% (5 bar of H 2, MeOH, 100 °C). In-situ high-pressure NMR spectroscopy in catalytic conditions shows that the catalytically active species is generated by deorthometalation rather than by H 2 reductive elimination. 1 H NMR spectroscopy also suggests that the two C N groups in MeQ are hydrogenated at comparable rates.