1: 75 percent / methanesulfonic acid / 3.5 h / 70 °C / other reagent: polyphosphoric acid 2: 72 percent / p-toluenesulfonic acid monohydrate, chloranil / benzene / 12 h / Ambient temperature; other reactant: 9-benzyl-2-formyl-4-oxo-1,2,3,4-tetrahydro-β-carboline, other reagent: benzoquinone, other reaction time 3: 74 percent / m-chloroperbenzoic acid / CH2Cl2 / 24 h / Ambient temperature View Scheme

1: 75 percent / methanesulfonic acid / 3.5 h / 70 °C / other reagent: polyphosphoric acid 2: 72 percent / p-toluenesulfonic acid monohydrate, chloranil / benzene / 12 h / Ambient temperature; other reactant: 9-benzyl-2-formyl-4-oxo-1,2,3,4-tetrahydro-β-carboline, other reagent: benzoquinone, other reaction time 3: 74 percent / m-chloroperbenzoic acid / CH2Cl2 / 24 h / Ambient temperature 4: 61 percent / triethylamine / acetonitrile / 5 h / 70 °C 5: 97 percent / KOH / acetonitrile; H2O / 14 h / Ambient temperature 6: 2.) SiO2 / 1.) THF, hexane, -50 deg C, 30 min, 2.) 1 week; other reagent: H(1+) View Scheme

1: 75 percent / methanesulfonic acid / 3.5 h / 70 °C / other reagent: polyphosphoric acid 2: 72 percent / p-toluenesulfonic acid monohydrate, chloranil / benzene / 12 h / Ambient temperature; other reactant: 9-benzyl-2-formyl-4-oxo-1,2,3,4-tetrahydro-β-carboline, other reagent: benzoquinone, other reaction time 3: 74 percent / m-chloroperbenzoic acid / CH2Cl2 / 24 h / Ambient temperature 4: 61 percent / triethylamine / acetonitrile / 5 h / 70 °C 5: 97 percent / KOH / acetonitrile; H2O / 14 h / Ambient temperature 6: 90 percent / HCl / CH2Cl2 / 1.) room temperature, 24 h, 2.) reflux, 10 h View Scheme