Two diastereomers of 9-(2,6-dichlorophenyl)-4a-hydroxy-3,3,6,6-tetramethyl-1,2,3,4,4a,5,6,7,8,9a-decahydroxanthene-1,8-dione in the same crystal.

The reaction of dimedone with 2,6-dichlorobenzaldehyde leads to the title compound, C(23)H(26)Cl(2)O(4). In principle, the reaction could yield eight different stereoisomers. We have found four of them in the same crystal as two enantiomeric pairs of diastereomers, which means that the asymmetric unit is built up of two different diastereomers. Two of the three chiral centres display the same configuration, while the third is different in the two molecules in the asymmetric unit. The packing of the molecules is stabilized by hydrogen bonds between the hydroxy group and the carbonyl group attached to the cyclohexene ring, forming chains in which the different diastereomers alternate.