1: 1.) Et3N / 1.) THF, -5 deg C to 0 deg C, 2.) hexane, 1 h, 20 deg C 2: 4-dimethylaminopyridine / tetrahydrofuran / 2 h / 20 °C 3: 60 percent / anhydrous oxalic acid / 0.25 h / 110 - 120 °C View Scheme

Multi-step reaction with 2 steps 1: 1.) Et3N / 1.) THF, -5 deg C to 0 deg C, 2.) hexane, 1 h, 20 deg C2: 4-dimethylaminopyridine / tetrahydrofuran / 2 h / 20 °C