1: 1) t-BuOK / 1) THF, toluene, 10 min, 2) toluene, 0 deg C, 20 min 2: 1) CH2Cl2, molecular sieves 3A, UV, 0 - 5 deg C 3: 74 percent / 1 M BuOK / tetrahydrofuran; 2-methyl-propan-2-ol / Heating 4: CF3COOH, H2O 5: diethyl phosphorocyanidate, triethylamine / dimethylformamide View Scheme

1: 1) t-BuOK / 1) THF, toluene, 10 min, 2) toluene, 0 deg C, 20 min 2: 1) CH2Cl2, molecular sieves 3A, UV, 0 - 5 deg C 3: 74 percent / 1 M BuOK / tetrahydrofuran; 2-methyl-propan-2-ol / Heating 4: CF3COOH, H2O View Scheme