1: 4-(N,N-dimethlyamino)pyridine / toluene / 24 h / 25 - 30 °C 2: sulfuric acid / water; tetrahydrofuran / 40 h / 0 - 30 °C View Scheme

<b>Multi-step reaction with 2 steps<br /> </b>1.1: toluene-4-sulfonic acid / 110 - 115 &deg;C<br />1.2: 24 h / 110 - 115 &deg;C<br />2.1: triethylamine / dichloromethane / 0 - 5 &deg;C<br /> <br /> &nbsp;

<b>Multi-step reaction with 3 steps<br /> </b>1.1: hexafluorophosphoric acid / methanol / 20 h / 65 - 67 &deg;C<br />2.1: toluene-4-sulfonic acid / 110 - 115 &deg;C<br />2.2: 24 h / 110 - 115 &deg;C<br />3.1: triethylamine / dichloromethane / 0 - 5 &deg;C<br /> <br /> &nbsp;