boron tribromide in dichloromethane T=-78°C; 0.333333 h;

toluene-4-sulfonic acid in toluene Heating;

toluene-4-sulfonic acid T=110°C; 2.5 h;

1: 1.) lithium diisopropylamide / 1.) THF, -78 deg C, 20 min, 2.) THF, -78 deg C -> room temperature 2: 71 percent / p-toluenesulfonic acid / toluene / Heating View Scheme

1.1: 76 percent / polyphosphoric acid / 2 h / 90 °C 2.1: diethyl oxalate; NaOMe / toluene / 1 h / 20 °C 2.2: 72 percent / aq. H2O2; KOH / methanol / 16 h / 20 °C 3.1: 81.7 percent / pyridine / diethyl ether / 20 °C 4.1: 76 percent / acetic anhydride / 2 h / Heating 5.1: 75 percent / boron tribromide / CH2Cl2 / 0.33 h / -78 °C 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

1: 81.7 percent / pyridine / diethyl ether / 20 °C 2: 76 percent / acetic anhydride / 2 h / Heating 3: 75 percent / boron tribromide / CH2Cl2 / 0.33 h / -78 °C View Scheme

1: 76 percent / acetic anhydride / 2 h / Heating 2: 75 percent / boron tribromide / CH2Cl2 / 0.33 h / -78 °C View Scheme