1: 1) (COCl)2, DMSO 2) Et3N / 1) CH2Cl2, -78 to -40 deg C 2: NaClO2, NaH2PO4, 2-methyl-2-butene / 2-methyl-propan-2-ol / 0.5 h / 0 to 20 deg C 3: 66 percent / HOBT, 1-(3-dimethylaminopropyl)-ethylcarbodiimide*HCl / CH2Cl2; dimethylformamide / 10 h / 0 to 20 deg C 4: 54 percent / TBAF / tetrahydrofuran / 1.5 h / 20 °C View Scheme