1: phosphoric acid / 3 h 2: N,N-dimethyl-formamide / 4 h / Reflux View Scheme

1.1: phosphoric acid / 3 h 2.1: N,N-dimethyl-formamide / 4 h / Reflux 3.1: sodium hydride / dimethyl sulfoxide; paraffin oil / 0.17 h / 20 °C / Inert atmosphere 3.2: 0.83 h / 40 °C View Scheme

toluene-4-sulfonic acid in toluene Heating / reflux;