1: 57 percent / triethylamine; 4-(dimethylamino)pyridine / CH2Cl2 / 7 h 2: 2,6-lutidine; 4-(dimethylamino)pyridine / CH2Cl2 / 23 h 3: triethylamine / CH2Cl2 / 24 h / 0 °C 4: 76 percent / tetra-n-butylammonium fluoride / tetrahydrofuran / 0.5 h / 0 °C View Scheme