1: 4-dimethylaminopyridine / tetrahydrofuran / 2 h / 20 °C 2: 60 percent / anhydrous oxalic acid / 0.25 h / 110 - 120 °C View Scheme

With  4-(N,N-dimethlyamino)pyridine in  tetrahydrofuran T=20°C; 2 h;