Redetermination and absolute configuration of berkeleydione

The crystal structure of the title compound, berkeleydione [systematic name; (5aS,7R,9S,11R,11aS)-methyl 9-hydroxy-1,1,5,7,9,11a-hexamethyl-14-methylidene-3,8,10-trioxo-1,3,4,5a,6,7,8,9,10,11,11a,12-dodecahydro-7,11-methanocyclo-octa[4,5]cyclohepta[1,2-c]pyran-11-carboxylate], C₂₆H₃₂O₇, has been reported previously [Stierle et al. (2004). Org. Lett. 6,1049-1052]. However, the absolute configuration could not be determined from the data collected with Mo Ka radiation and has now been determined by refinement of the Flack parameter with data collected using Cu Kα radiation. It is in agreement with the previous circular dichroism assignment, and the crystal packing is similar to that described previously.