1: oxalyl chloride, DMSO / CH2Cl2 / 0.42 h / -60 °C 2: 1.) di-n-butylboryl triflate, diisopropylethylamine / 1.) CH2Cl2, -78 deg C, 30 min, 2a.) -78 deg C, 1 h, 2b.) 0 deg C, 1.5 h 3: 72 percent / pyridine, CrO3 / CH2Cl2 / 0.25 h 4: 84 percent / 40percent aq. HF / acetonitrile / 1 h / 25 °C 5: 1 N aq. LiOH / 1,2-dimethoxy-ethane / 0.75 h / 25 °C View Scheme