1: 1.) ethyl chloroformate; 2.) P(OMe)3; 3.) TiCl4 / 1.) THF, -10 deg C, 5 min; 2.) THF, r.t., 15 h; 3.) CH2Cl2, reflux, 36 h 2: 30percent H2O2 / acetic acid / 12 h / 60 - 70 °C 3: 70 percent / Ac2O, 1 M NaOH / 5 h / Heating 4: 69 percent / POCl3 / 3 h / Heating View Scheme

chloroformic acid ethyl ester; titanium tetrachloride; phosphorous acid trimethyl ester 1.) THF, -10 deg C, 5 min; 2.) THF, r.t., 15 h; 3.) CH2Cl2, reflux, 36 h; Yield given. Multistep reaction;