1: 100 percent / CF3COOH / CH2Cl2 / 2 h / Ambient temperature 2: oxalyl chloride, DMF / CH2Cl2 / 1 h / Ambient temperature 3: pyridine / CH2Cl2; tetrahydrofuran / 2 h / Ambient temperature View Scheme

trifluoroacetic acid in dichloromethane 2 h; Ambient temperature;