1: 60 percent / tetrahydrofuran / 2 h / -78 °C 2: 1.) (COCl)2, DMSO, 2.) Et3N / 1.) CH2Cl2, -78 deg C, 15 min, 2.) -78 deg C -> room temperature View Scheme

oxalyl dichloride; dimethyl sulfoxide; triethylamine 1.) CH2Cl2, -78 deg C, 15 min, 2.) -78 deg C -> room temperature; Yield given. Multistep reaction;