2,2,2-Trichloroethyl chloroformate (0.077 mL, 0.57 mmol) was added to a solution of Intermediate 12c (200 mg, 0.57 mmol) and DIPEA (0.31 mL, 1.81 mmol) in THF (5 mL), and the mixture stirred for 3 h. The mixture was then partitioned between water (10 mL) and EtOAc (3×15 mL), and the combined organic extracts dried (Na2SO4). The solvent was evaporated and the residue triturated under pentane and filtered to give the title compound as a yellow solid (215 mg, 72%). LCMS (Method 1): Rt 2.89 min, m/z 523/525 [MH+]
