(3R,4S,5S)-4-Hydroxy-3-methyl-5-[(2S,3R)-3-methylpent-4-en-2-yl]tetrahydrofuran-2-one

The title compound, C11H18O3, was synthesized to prove the relative configuration of the corresponding acyclic C1—C8 stereopentade. It crystallizes with two molecules in the asymmetric unit, which show only slight differences. The molecules are linked via O—H⋯O hydrogen bonds, resulting in two crystallographically independent chains of molecules propagating in the a-axis direction. The absolute configuration was known from the synthesis.

The title compound, C 11 H 18 O 3 , was synthesized to prove the relative configuration of the corresponding acyclic C1-C8 stereopentade. It crystallizes with two molecules in the asymmetric unit, which show only slight differences. The molecules are linked via O-HÁ Á ÁO hydrogen bonds, resulting in two crystallographically independent chains of molecules propagating in the a-axis direction. The absolute configuration was known from the synthesis.
There are two molecules of (I) in the asymmetric unit (Figs. 1 and 2) with similar conformations. In the crystal, the molecules interact via O-H···O hydrogen bonds (Table 1) to form two independent chains, both propagating in [100].

Experimental
The title compound, (I), was synthesized from the corresponding anti-aldol adduct, (II), using tetrabutylammonium fluoride (TBAF) (Corey et al., 1972) for the removal of the silyl protecting group. The subsequent lactonization proceeded in situ.
TBAF (1 M in tetrahydrofuran, 0.82 ml, 3.0 eq) was added to a solution of the diastereomeric mixture of (II) (dr = 7/3, 120 mg, 0.27 mmol, 1.0 eq) in dry tetrahydrofuran (2 ml) at 273 K. The mixture was stirred at 273 K for 15 min and then at 298 K for 30 min. The reaction was quenched by the addition of saturated aqueous NaHCO 3 solution. The phases were separated, and the aqueous phase was extracted with CH 2 Cl 2 . The combined organic layers were dried over MgSO 4 and concentrated under reduced pressure. Flash chromatography (isohexane/ethyl acetate 20/1 to 10/1) afforded (I) as a single diastereomer and additionally a mixture of (I) and the minor diastereomer with an overall yield of 72% (38.7 mg, 0.195 mmol) as colourless crystals. Single crystals of (I) were obtained by vapor diffusion recrystallization technique from isohexane and ethyl acetate to yield colourless cuboids: mp 412 K; R f 0.33 (cyclohexane/ethyl acetate 2/1); 1 H NMR

Refinement
Anomalous dispersion was negligible and Friedel pairs were merged before refinement. The H atoms were geometrically placed (C-H = 0.93-0.98Å, O-H = 0.82Å) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C, O). Fig. 1. : The molecular structure of molecule one of (I), with displacement ellipsoids for the non-hydrogen atoms shown at the 30% probability level.

Special details
Geometry. All e.s. 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 Rfactors(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.