Two diastereomers of 9-(2,6-dichlorophenyl)-4a-hydroxy-3,3,6,6-tetra-methyl-1,2,3,4,4a,5,6,7,8,9a-deca-hydroxanthene-1,8-dione in the same crystal

The reaction of dimedone with 2,6-dichlorobenzaldehyde leads to the title c ompound, C23H26Cl2O4. In principle, the reaction could yield eight differen t stereoisomers. We have found four of them in the same crystal as two enan tiomeric pairs of diastereomers, which means that the asymmetric unit is bu ilt up of two different diastereomers. Two of the three chiral centres disp lay the same configuration, while the third is different in the two molecul es in the asymmetric unit. The packing of the molecules is stabilized by hy drogen bonds between the hydroxy group and the carbonyl group attached to t he cyclohexene ring, forming chains in which the different diastereomers al ternate.