A sample was purified by flash column chromatography on silica gel using 0 to 25% iPrOAc in heptane to obtain an analytically pure sample as a colorless oil which matched reported literature. 9 TLC (25% iPrOAc in heptane, Rf): 0.41 (UV). The temperature was then cooled to 0 °C and NBS [6.9 kg, 39.0 mol, 1.0 equiv.] was slowly added.