1: Amberlyst-15 / methanol / 12 h / Ambient temperature 2: 85 percent / pyridine / 12 h / 70 °C 3: 0.3 N aq.LiOH / tetrahydrofuran / 120 h / 30 °C 4: benzenesulfonyl chloride, pyridine / 12 h / 0 °C 5: 5.4 mg / HOAc, H2O / 7 h / 50 °C View Scheme