1: (COCl)2; Et3N / tetrahydrofuran / -20 °C 2: 92 percent / KN(TMS)2 / tetrahydrofuran / -20 °C 3: 75 percent / TMSCl / H2O; CH2Cl2 View Scheme

oxalyl dichloride; triethylamine in tetrahydrofuran T=-20°C;