Crystal structure of (−)-(S)-4-[(2S,3S,4S,Z)-3-hydroxy-4-methylhept-5-en-2-yl]-1,3-dioxolan-2-one

The title compound consists of an anti,anti,anti-stereotetrad with a 1,2-carbonate and an alkene motif.


Chemical context
The title compound was obtained as part of our studies toward the synthesis of (À)-dolabriferol and (À)-dolabriferol B (Ciavatta et al., 1996;Jimé nez-Romero et al., 2012), using an epoxide-based approach for the stereotetrad construction. Polypropionate chains are structural motifs consisting of alternating methyl and hydroxy groups within an aliphatic framework (Torres et al., 2004(Torres et al., , 2009Tirado et al., 2005, Rodríguez et al., 2006. Their structure is found in various natural products, many of them possessing a wide range of biological activity, typically antibiotic, antitumor, antifungal, antiparasitic, among others (Rohr, 2000). Different methodologies for the synthesis of polypropionates have been developed, with aldol and aldol-related chemistry being the most used (Schetter & Mahrwald, 2006).
In our laboratory, we have developed an epoxide-based methodology for the construction of polypropionates, consisting of a reiterative sequence of three steps. Our approach involves a regioselective epoxide cleavage with an alkynyl aluminium reagent (Torres et al., 2005) or Grignard reagent (Rodríguez et al., 2006), cis or trans reduction of the alkyne (if needed), and the stereoselective epoxidation of the resulting alkenol for the elaboration of each propionate unit. In this approach, the configuration of the hydroxyl group is derived from the absolute configuration of the epoxide precursor, while the syn/anti relative configuration of the ISSN 2056-9890 methyl and hydroxyl groups is derived from the epoxide geometry. One of the advantages of this methodology is that it is a substrate-controlled synthesis; the only enantiomeric step in this sequence is the first epoxidation (Katsuki & Sharpless, 1980).

Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1. The alkyl back bone has a typical zigzag conformation with two of the three methyl groups, those located on C4 and C6, anti to one another. Likewise, the hydroxy group located on C5 is in an anti relative conformation with respect to the methyl groups. The five-membered ring (O2/O3/C1-C3) has a twisted conformation on bond C2-C3 [puckering parameters Q(2) = 0.137 (2) Å and '(2) = 307.4 (10) ].

Supramolecular features
The conformational distance between the hydroxyl group and the carbonyl moiety does not allow intramolecular hydrogenbond formation, therefore, hydrogen bonding is observed through intermolecular interactions alone (

Figure 2
A view along the a axis of crystal packing of the title compound, with hydrogen bonds shown as dashed lines (see Table 1).

Figure 1
The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.
acetate:hexanes solution of the title compound at room temperature over a period of two days. NMR analyses were performed on a Bruker AV-500 spectrometer using Chloroform-d as solvent (CDCl 3

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2 (Macrae et al., 2008); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

(-)-(S)-4-[(2S,3S,4S,Z)-3-hydroxy-4-methylhept-5-en-2-yl]-1,3-dioxolan-2-one
Crystal data 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.