1.1: diethyl oxalate; NaOMe / toluene / 1 h / 20 °C 1.2: 72 percent / aq. H2O2; KOH / methanol / 16 h / 20 °C 2.1: 81.7 percent / pyridine / diethyl ether / 20 °C 3.1: 76 percent / acetic anhydride / 2 h / Heating View Scheme

1.1: diethyl oxalate; NaOMe / toluene / 1 h / 20 °C 1.2: 72 percent / aq. H2O2; KOH / methanol / 16 h / 20 °C 2.1: 81.7 percent / pyridine / diethyl ether / 20 °C 3.1: 76 percent / acetic anhydride / 2 h / Heating 4.1: 75 percent / boron tribromide / CH2Cl2 / 0.33 h / -78 °C View Scheme