Multi-step reaction with 3 steps 1: 84 percent / diphenyl-azidophosphate, NEt3, molecular sieve / 2-methyl-propan-2-ol; H2O / 36 h / Heating2: 2 N NaOH / pentan-1-ol / 120 h / Heating3: 75 percent / carbonyldiimidazol; 4-(dimethylamino)pyridine / CH2Cl2 / 48 h