Multi-step reaction with 4 steps 1: xylene / 48 h / Heating2: 1.) dicyclohexylcarbodiimide, p-toluenesulphonic acid; 2.) g. acetic acid / 1.) pyridine, 24 h; 2.) 2 h, r.t., 0 degC, overnight3: 95 percent / sodium sulphate / CH2Cl2 / reflux 1 h, r.t. 10 h4: xylene / 24 h / Heating