1: 88 percent / 2,3-dichloro-5,6-dicyano-1,4-benzoquinone / CH2Cl2; H2O / 20 °C 2: 82 percent / zinc bromide / CH2Cl2 / 6 h / 20 °C View Scheme

zinc dibromide in dichloromethane T=20°C; 6 h;