The free base of 48 is prepared from 47 (1.75 g, 3.95 mmol), solid supported Hünig's base (2.22 g) and α-chloroethyl chloroformate (1.62 mL) in anhydrous DCM (30 mL) following General Procedure 3. Purification by ion exchange chromatography followed by flash column chromatography (eluent, MeOH/DCM 1/99 to 20/80 [v/v]) gives the free base as a viscous oil (805 mg, 58%) which is converted into 48 following General Procedure 4. MW 387.95; C23H29NO2.HCl; 1H NMR (CD3OD): δ 7.66-7.40 (1H, m) 7.19-7.47 (8H, m), 3.92 (1H, dd, 13 Hz, 3.5 Hz), 3.59-3.67 (2H, m), 3.05-3.16 (4H, m), 2.93 (1H, td, 13 Hz, 3.5 Hz,), 2.59 (1H, t, 12 Hz), 1.98-1.88 (1H, m), 1.55-1.19 (8H, m); LCMS: (12 minute method) m/z 351 [M−HCl+H]+, RT 5.68 min.
