The enantiomers of 2a and those of its brominated derivative 2c were separated using high-performance liquid chromatography (HPLC) (Figures ). An X-ray diffraction analysis revealed that the first fraction of 2c is the (M,M)-enantiomer with a Flack parameter of 0.002(7) (Figure ). The palladium-catalyzed debromination of (M,M)-2c with HCOOH/NEt3 afforded (M,M)-2a (Scheme S1), which is identical to the first eluted fraction from the HPLC resolution of 2a (Figure ). The activation barrier of the racemization process of 2a was evaluated by monitoring the decrease of the circular dichroism (CD) signals upon heating. This analysis afforded an activation enthalpy (ΔH) of 29.8 kcal mol -1 and an activation entropy (ΔS) of -11 cal K -1 mol -1 (Figures ). These results indicate that 2a is configurationally stable at room temperature.