1: silica gel / benzene; H2O / 48 h 2: 96 percent / toluene-p-sulphonic acid / benzene / 2 h / Heating 3: 90 percent / 2,3-dichloro-5,6-dicyano-p-benzoquinone View Scheme

1: silica gel / benzene; H2O / 48 h 2: 96 percent / toluene-p-sulphonic acid / benzene / 2 h / Heating View Scheme