Scheme 2.

Three different synthesis procedures for the introduction of the nitrile group in position 3 of the indole core structure. Reagents and conditions: (a) oxalyl chloride, diethyl ether, rt, 6 h; (b) hydroxyl ammonium chloride, sodium acetate, ethanol/water, reflux, 6–9 h (compounds 6a–c,6k–l); (c) 1. acetonitrile, 0 °C to rt, 4 h; 2. dimethylformamide, acetonitrile, rt, 2 h (compounds 6d,6p–r); and (d) BF₃·OEt₂, 1,2-dichloroethane or toluene, 100 °C (bath temperature) or reflux, 15–48 h (compounds 6e–j,6m–o,6s).