tert-Butanol → tert-Butyl {1-(morpholin-4-ylcarbonyl)-5-[4-(trifluoromethyl)phenyl]piperidin-3-yl}carbamate

Activated molecular sieves 4 Å (about 10 g), 2.16 ml (15.5 mmol) of triethylamine and 3.92 g (14.2 mmol) of diphenyl phosphorazidate were added to the carboxylic acid from Example 55A (5.00 g, 12.9 mmol) in tert-butanol (235 ml), and the mixture was stirred under reflux overnight. The reaction solution was cooled, and the molecular sieves were then filtered off and washed thoroughly with ethyl acetate. The solvent was removed under reduced pressure and the residue was taken up in ethyl acetate. After washing with 2 N aqueous hydrogen chloride solution, saturated aqueous sodium bicarbonate solution and water, the organic phase was dried over magnesium sulphate, filtered and concentrated under reduced pressure. The crude product was used for the next step without further purification. Yield: 5.53 g (89% of theory)