1: 90 percent / p-toluenesulfonic acid / dimethylformamide / 3 h / 60 °C 2: 82 percent / pyridine / 52 h / 60 °C 3: 89 percent / 80percent aq. acetic acid / 1.5 h / 70 °C 4: 40 percent / sodium acetate / H2O; 2-methoxy-ethanol / 1.5 h / 120 °C View Scheme