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

The orthometalated dihydride complex fac-exo-(R)-[IrH2{C6H4C*H(Me)N(CH2CH2PPh2)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 H2, 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 H2 reductive elimination. 1H NMR spectroscopy also suggests that the two CdN groups in MeQ are hydrogenated at comparable rates.