Crystal structure of 3a,6,6,9a-tetramethyldodecahydronaphtho[2,1-b]furan-2-ol

The title compound (common name: sclaral), C16H28O2, is a sclareolide derivative, which was synthesized from sclareolide itself. In the molecule, the two six-membered rings, A and B, of the labdane skeleton adopt chair conformations and the five-membered O-containing heterocyclic ring C displays an envelope conformation, with the methine C atom of the fused C—C bond as the flap. In the crystal, molecules are linked by O—H⋯O hydrogen bonds, forming chains propagating along [100].


S1. Comment
The title compound, sclaral, is an important reaction intermediate in the synthesis of some natural products. It is used as a precursor of borono-sclareolide which makes the direct coupling of a terpenoid "donor" with a non-terpenoid "acceptor" possible (Dixon et al., 2012). It is also used to produce analogs of hongoquercin A, an antibiotic of fungal origin (Michaudel et al., 2015;Sun et al., 2013). Moreover, sclaral is an intermediate in the production of important natural products, such as (+)-premnalane A (Margaros et al., 2007). The title compound has been synthesized and we report herein on its crystal structure, The molecular structure of the title compound is shown in Fig. 1. The molecule possesses a highly rigid structure, composed of three main rings (A/i>, B and C). The six-membered rings, A/i> (C5/C6/C8-C11) and B (C1-C6), adopt chair conformations, while the five-membered O-containing heterocyclic ring C (C1/C2/C14/C15/O1) displays an envelope conformation, in which atom C1 is the flap.
In the crystal, molecules are linked via O-H···O hydrogen bonds forming chains propagating along the a axis direction (Table 1 and Fig. 2).
Water was then slowly added until the bubbles vanished then the temperature of the mixture was allow to rise to rt. the mixture was stirred at rt for 30min, and then extracted with CH 2 Cl 2 (3 × 100 ml). The combined organic extracts were washed with saturated aqueous NaHCO 3 solution (3 × 50 ml) and washed with brine (3 × 50 ml), dried over MgSO 4 , filtered and concentrated under reduced pressure, affording the title compound, sclaral (yield: 9.37 g, 93 %, 3.7:1 lactol:aldehyde) as a white solid. Spectroscopic and analytical data matches reported previously (Margaros et al., 2007).
The white solid was recrystallized from EtOH to afford colourless crystals.

S3. Refinement
The CH H atoms (H1, H5 and H15) and the hydroxyl H atom (H1O) were located in a difference Fourier map. The CH H atoms were freely refined while the OH H atom was refined with U iso (H) = 1.5U eq (O  View along the a axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1), and C-bound H atoms have been omitted for clarity.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.