1: 67 percent / Dowex 50W-X8 (H+) / CHCl3 / 3 h 2: 5.0 mg / pyridine, 4-dimethylaminopyridine / tetrahydrofuran / 43 h 3: 81 percent / Dowex 1-X8 (OH(1-)), methanol / 2 h / 0 °C View Scheme