rac-8a’-Methyl-3′,4′,8′,8a’-tetrahydro-2′H-spiro[[1,3]dioxolane-2,1′-naphthalen]-6′(7′H)-one

The title racemic compound, C13H18O3, a common precursor in the total synthesis of terpenes, crystallizes with two molecules in the asymmetric unit. The crystal structure is made up of triple chains, formed by weak intermolecular C—H⋯O contacts, propagating in the a-axis direction.

The title racemic compound, C 13 H 18 O 3 , a common precursor in the total synthesis of terpenes, crystallizes with two molecules in the asymmetric unit. The crystal structure is made up of triple chains, formed by weak intermolecular C-HÁ Á ÁO contacts, propagating in the a-axis direction.

Related literature
For the synthesis of the title compound, see: Smith et al. (2007). For the crystal structure of the educt, 9-methyl-Á 5,10decalin-1,6-dione, see: Jones et al. (1973). For application of the title compound as a precursor in the synthesis of terpenes, see: Foot et al.

Comment
The title compound crystallized at 200 K with two formula units (1 and 2), of the same handedness, in the asymmetric unit ( Fig. 1). The conformation of the two molecules is nearly identical, apart from the dioxolane rings which are of opposite twist (see Inset in Fig. 1). In molecule 1 the dioxalane ring has an envelope conformation on atom O12, while in molecule 2 the envelope conformation is on atom C213. In both molecules the cyclohexane rings adopt chair conformations, while the cyclohexanone rings are somewhat flattened due to the presence of the carbonylic carbon and the double bond.
In the crystal molecules are linked by four different sets of rather weak C-H···O contacts (Fig. 2, Table 1). This results in the formation of triple-chains running along the a axis, with central strands of molecules of conformation 1 flanked by molecules of conformation 2 (Figs. 2 and 3).

Experimental
The title compound was prepared from racemic Wieland-Miescher ketone according to a described procedure (Smith et al., 2007), with a minor modification to the purification method. After extraction the raw product was purified by flash chromatography (2% i-PrOH in petroleum ether) and the solvent of the so obtained fractions was distilled off. The portion containing a mixture of the title compound and ethylene glycol was kept at room temperature for several weeks, whereupon colourless acicular crystals developed.