1: 71 percent / triethylamine, 4-dimethylaminopyridine / 48 h / Ambient temperature 2: 40 percent / triethylamine, 4-dimethylaminopyridine / 7 h / ice-NaCl bath 3: 70 percent / aq. acetic acid / tetrahydrofuran / 4 h / Ambient temperature View Scheme