1: 0.738 g / oxalic acid / methanol / 6 h / Ambient temperature 2: 1.068 g / Et3N / tetrahydrofuran / 2 h / Ambient temperature 3: 997 mg / LiBr / tetrahydrofuran / 15 h / Ambient temperature View Scheme

With  oxalic acid in  methanol 6 h;  Ambient temperature;   

Multi-step reaction with 2 steps 1: 0.738 g / oxalic acid / methanol / 6 h / Ambient temperature2: 1.068 g / Et3N / tetrahydrofuran / 2 h / Ambient temperature