Crystal structure of (±)-(4RS,5RS,7SR)-4-[(1RS,2RS,3RS,6RS)-3-benzoyloxy-2-(2-hydroxyethyl)-6-methoxymethoxy-2-methylcyclohexyl]-8,10,10-trimethyl-2-oxo-1,3-dioxaspiro[4.5]dec-8-en-7-yl benzoate benzene monosolvate

In the title compound, the ring conformations of the tricycles are in an envelope, a half-chair and a chair. In the crystal, intermolecular O—H⋯O and C—H⋯O hydrogen bonds and C—H⋯π interactions link the molecules into a three-dimensional architecture.


Chemical context
Paclitaxel is a well-known natural diterpenoid containing a taxane framework (tricyclo[9.3.1.0 3,8 ]pentadecane; Fig. 1), with potent antitumor activity (Wall & Wani, 1995). This unique and complicated structure has attracted significant interest, and a large number of synthetic studies have been reported. In these researches, whereas some structure data after cyclization into taxane or taxoid derivatives are available (x 4), precursors just before cyclization are very few. The title compound has been obtained in our synthetic study of paclitaxel as a cyclization precursor to build the taxane skeleton (Fukaya et al., 2014).

Figure 3
The molecular conformation indicating the intramolecular C-HÁ Á ÁO interactions with dashed lines. Only H atoms involved in hydrogen bonds are shown for clarity. The benzene solvent molecule has been omitted. Table 1 Hydrogen-bond geometry (Å , ).
Cg is the centroid of the C47-C52 ring.

Synthesis and crystallization
The title compound was obtained in a synthetic study on paclitaxel. The cyclohexene unit (C5-C10) was provided according to the reported procedure (Nicolaou et al., 1995), and coupled with the substituted cyclohexane unit (C24-C29) synthesized from 3-methylanisole (Fukaya et al., 2014) by a Shapiro reaction (Nicolaou et al., 1995). Further manipulation of the functional groups afforded the title compound, which was purified by silica gel column chromatography. Colorless crystals were grown from a benzene solution under a pentanesaturated atmosphere by slow evaporation at ambient temperature.

Figure 5
Core substructures for database survey; (a) 6,6, geometrically with C-H = 0.95-1.00 Å , and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). The H atom of hydroxy group (O41) was placed guided by difference maps and then treated as riding, with O-H = 0.84 Å and with U iso (H) = 1.5U eq (O). 13 problematic reflections were omitted from the final refinement.