1: 1.) O3, 2.) Zn-dust, HOAc / 1.) MeOH, -78 deg C, 0.5 h, 2.) MeOH, RT, 48 h 2: 38 percent / Et3N / benzene / 0 °C 3: 55 percent / 2,3-dichloro-4,5-dicyanobenzoquinone / dioxane / 3 h / Heating 4: 0.01 N HCl / methanol; H2O / 2 h / 105 °C 5: Bu4NBr, 9 M aq. HBr / 0.75 h / 110 °C View Scheme