1: diisopropylamine, butyllithium / tetrahydrofuran; hexamethylphosphoric acid triamide / - 20 deg C, 20 min; r.t., overnight 2: 30percent aq. oxalic acid / tetrahydrofuran / 1.5 h / Heating 3: Zn-Hg, HCl / toluene / 10 h / Heating 4: 47percent HBr / acetic acid / 10 h / 130 °C View Scheme