Secondary alcohol 11 (100 mg, 0.182 mmol) , dichloromethane (10 mL), and para­toluenesulfonic acid (4.0 mg, 0.020 mmol) were added to a round­bottomed flask and stirred at 22 oC for four hours. The reaction mixture was then quenched with saturated aqueous sodium bicarbonate (10 mL). The organic layer was then extracted with ethyl acetate (3 x 20 mL), washed with brine (20 mL), and dried over anhydrous sodium sulfate. The solid product was then collected via vacuum filtration. The solid was dissolved in dichloromethane and purified via column chromatography using an eluent of ethyl acetate : petroleum ether (1:6 ­­> 1:2). Nitrogen gas was used to evaporate the solvent, resulting in a white solid polycyclic acetal 21.