1: 72 percent / hydrochloric acid / tetrahydrofuran / 1 h / Heating 2: 66 percent / imidazole / dimethylformamide / 13 h / 60 °C 3: 89 percent / pyridine / 0.5 h / Ambient temperature 4: 90 percent / tetra-n-butylammonium fluoride / tetrahydrofuran / 0.5 h / Ambient temperature 5: 47 percent / 1,1,3,3-tetramethylurea, stannous triflate, 4A molecular sieves / CH2Cl2 / 16 h / Ambient temperature 6: 95 percent / sodium methoxide / methanol / 1 h / Ambient temperature View Scheme

toluene-4-sulfonic acid in methanol; dichloromethane 14 h;