1: 1.) oxalyl chloride, DMSO 2.) triethylamine / 1.) CH2Cl2, -60 deg C, 15 min 2.) -60 deg C, 15 min 2: 78 percent / BF3.Et2O, bis(trimethylsilyl)peroxide / CH2Cl2 / 1.5 h / Ambient temperature; 2 3: 42 percent / boron trichloride / CH2Cl2; hexane / 4 h / -78 °C View Scheme