1: toluene-4-sulfonic acid / toluene / 5 h / |Reflux 2: acetic anhydride / formic acid / 5 h / 20 °C 3: trichlorophosphate; triethylamine / tetrahydrofuran / 2 h / -78 - 20 °C / |Inert atmosphere View Scheme

toluene-4-sulfonic acid in toluene 5 h; Reflux;