1: tetrahydrofuran; hexamethylphosphoric acid triamide / 18 h / Ambient temperature 2: 56 percent / trimethylsilyl triflate / tetrahydrofuran; hexamethylphosphoric acid triamide; diethyl ether / 1.) -20 deg C, 15 min.; 2.) -40 deg C, 2 h.; 3.) -40 deg C, 1 h. View Scheme

trimethylsilyl trifluoromethanesulfonate; 1,1'-carbonyldiimidazole 1.) THF, HMPA, RT, 18 h; 2.) -20 deg C; 3.) ether, -40 deg C, 3 h; Yield given. Multistep reaction;