To a stirred solution of 17 (2.8 g, 6.3 mmol) in dichloromethane (200 mL) was added TFA (20 mL, 26.2 mmol), and the reaction was left to stir at ambient temperature overnight. The reaction mixture was concentrated under reduced pressure and reconcentrated from dichloromethane (5 × 50 mL), affording the crude product as the TFA salt. This was partitioned between dichloromethane (50 mL) and saturated aqueous sodium hydrogen carbonate solution. The organic phase was separated, and the aqueous component was extracted with dichloromethane (5 × 50 mL). The combined organic extracts were washed with brine (2 × 100 mL), dried over anhydrous magnesium sulfate and concentrated under reduced pressure affording the title compound as a red oil (2.2 g, 99%