Crystal structure of (+)-(1S,5S,6S,7S,10S,11S,16S)-16-hydroxy-7-(methoxymethoxy)-11,15,18,18-tetramethyl-3,13-dioxo-2,4-dioxatetracyclo[12.3.1.01,5.06,11]octadec-14-en-10-yl benzoate

In the title compound, ring conformations in the tetracyclic system are twist, chair, half-chair and boat-chair forms. In the crystal, the intermolecular O—H⋯O hydrogen bonds connect the molecules into a helical chain, and the intermolecular C—H⋯O interactions link the chains into a three-dimensional architecture.

In the fused tetracyclic system of the title compound, C 29 H 36 O 9 , the fivemembered dioxolane ring adopts a twist conformation; the two adjacent C atoms deviate alternately from the mean plane of the other three atoms by À0.252 (6) and 0.340 (6) Å . The cyclohexane, cyclohexene and central cyclooctane rings show chair, half-chair and boat-chair forms, respectively. There are three intramolecular C-HÁ Á ÁO interactions supporting the molecular conformation, with one S(6) and two S(7) graph-set motifs. In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds connect the molecules into a helical chain running along the c-axis direction, generating a C(7) graph-set motif. The chains are further linked by intermolecular C-HÁ Á ÁO interactions to construct a three-dimensional network. There is no valid C-HÁ Á Á interaction.
The title compound, which has a fused tetracyclic core composed of a taxane skeleton with an external cyclic carbonate, was afforded as a chiral form in an improved synthesis of paclitaxel (Iiyama et al., 2021). Several closely related structures Oishi, Fukaya et al., 2015a,b) obtained in another synthetic pathway  have been reported previously as racemic crystals.
There is no valid C-HÁ Á Á interaction.

Synthesis and crystallization
The title compound was provided in an improved chiral synthesis of paclitaxel (Iiyama et al., 2021). The cyclohexene unit (C1/C14/C13/C12/C11/C15) was prepared according to the reported procedure  from cyclohexane-1,3-dione, while the tetrasubstituted chiral cyclohexane unit (C3-C8) was derived from 3-methoxytoluene (Fukaya et al., 2016). Coupling reaction of these two units by utilizing a Shapiro reaction  led to generate the taxane framework, and further manipulations of the functional groups afforded the title compound. Purification was carried out by silica gel chromatography, and colorless crystals were obtained from a benzene solution under pentane-saturated atmosphere, by slow evaporation at ambient temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were positioned 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 hydroxy H atom was located in a difference map and was allowed to refine as riding, with O-H = 0.84 Å , and with U iso (H) = 1.5U eq (O).  publCIF (Westrip, 2010) and PLATON (Spek, 2020).  (Parsons et al., 2013). Absolute structure parameter: 0.01 (7) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Problematic ten reflections (1 7 0, 0 9 1, 5 1 5, 0 0 8, 1 11 1, 2 7 0, -2 13 2, 2 1 7, 1 12 2, 2 13 2) with |I(obs)-I(calc)|/σW(I) greater than 10 have been omitted in the final refinement.