1: DDQ / CH2Cl2; H2O 2: oxalyl chloride in DMSO, Et3N 3: 65 percent / n-BuLi / 2-methyl-propan-2-ol; tetrahydrofuran 4: 17 percent / p-TsOH*H2O / ethanol; H2O 5: 80 percent / 1N aq. NaOH View Scheme