TFA (25 mL) was added to a solution of commercially available tert-butyl 3-oxo-2,3-dihydrospiro[indene-1,4′-piperidine]-1′-carboxylate (5.0 g, 16.6 mmol) in dichloromethane (25 mL) at 0° C. The reaction was then allowed to warm to rt for 30 min. The reaction was evaporated and dried under high vacuum for 30 min. The crude amine was dissolved in dichloromethane (25 mL) and triethylamine (6.9 mL, 49.8 mmol), trifluroacetic anhydride (2.6 mL, 18.3 mmol) and DMAP (20 mg, 0.17 mmol) were added in that order. The reaction was stirred at rt for 2 h and then diluted in dichloromethane and washed with water, sat. NH4Cl solution and brine; The organics were then dried (MgSO4), filtered and evaporated to give 19a as a light yellow solid (4.55 g, 92%). (M+H)+=298. 1H NMR (400 MHz, CDCl3) δ ppm 7.75 (d, J=7.6 Hz, 1H); 7.66 (t, J=7.0 Hz, 1H); 7.48 (d, J=7.9 Hz, 1H); 7.44 (t, J=7.5 Hz, 1H); 4.69 (d,J=15.9 Hz, 1H); 4.13 (d,J=14.1 Hz, 1H); 3.30 (t,J=11.8 Hz, 1H); 2.90 (t, J=13.4 Hz, 1H); 2.68 (m, 2H); 2.05 (dt, J=13.6, 3.8 Hz, 2H); 1.66 (d, J=13.9 Hz, 2H).
