1: Pyridine-2,5-dicarboxylic acid N-oxide With thionyl chloride in dichloromethane; N,N-dimethyl-formamide T=65°C; 2 h; 2: methanol in dichloromethane; N,N-dimethyl-formamide T=0°C;

bis-triphenylphosphine-palladium(II) chloride; sodium acetate; 1,4-di(diphenylphosphino)-butane in tetrahydrofuran T=150°C; P=11250.9 Torr; 6 h; Further byproducts given;

1.1: 99 percent / aq. Na2WO4; aq. H2O2 / 10 h / 80 - 85 °C 2.1: thionyl chloride / CH2Cl2; dimethylformamide / 2 h / 65 °C 2.2: 81.2 percent / CH2Cl2; dimethylformamide / 0 °C View Scheme

1: 3-chloro-pyridine-2,5-dicarboxylic acid dimethyl ester With tetrakis(triphenylphosphine) palladium(0) in toluene T=20°C; Suzuki coupling; 1 h; 2: 1H-indol-4-ylboronic acid With sodium carbonate in ethanol; toluene T=105°C; Suzuki coupling; 8 h; 3: ethanol With hydrogenchloride in diethyl ether T=20°C;

1.1: Pd(PPh3)4 / toluene / 1 h / 20 °C 1.2: aq. Na2CO3 / toluene; ethanol / 8 h / 105 °C 1.3: 91 percent / HCl / diethyl ether / 20 °C 2.1: 85 percent / Ca(BH4)2 / ethanol / 2 h / 20 °C 3.1: 92 percent / MnO2 / CH2Cl2 / 2 h / 20 °C View Scheme