(S)-6-{[(S)-2,2-Dimethyl-1,3-dioxolan-4-yl]methyl}-5,5-difluoro-5,6-dihydro-2H-pyran-2-one

The title compound, C11H14F2O4, is a γ,γ-gem-difluorinated α,β-unsaturated δ-lactone. The dioxolane five-membered ring and the lactone ring adopt half-chair conformations. There are two intermolecular C—H⋯O interactions involving the carbonyl group as an acceptor which stabilize the crystal structure.

The title compound, C 11 H 14 F 2 O 4 , is a ,-gem-difluorinated ,-unsaturated -lactone. The dioxolane five-membered ring and the lactone ring adopt half-chair conformations. There are two intermolecular C-HÁ Á ÁO interactions involving the carbonyl group as an acceptor which stabilize the crystal structure.
Financial support of this project by the Program for Changjiang Scholars and Innovative Research Teams in Universities (No. IRT0526) is acknowledged.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GK2220).
(S)-6-{[(S)-2,2-Dimethyl-1,3-dioxolan-4-yl]methyl}-5,5-difluoro-5,6-dihydro-2H-pyran-2-one Z. Yin, X. Deng, R. Yao, H. Li and P. Zhao Comment α,β-Unsaturated δ-lactone is a common structural unit of natural products with bioactivity. The structure-activity relationship (SAR) reveals that the unsaturated lactone often plays a key role in the bioactivity. The reason may be that the unsaturated lactone is an excellent potential Michael acceptor for natural nucleophiles such as the amino-acid residues. The title compound is an γ,γ-gem-difluorinated α,β-unsaturated δ-lactone, a better Michael acceptor for the electron-withdrawing of the difluoromethylene group. So it is a useful intermediate for synthesis of the fluorine-containing analogues of natural product with potential bioactivity. The title compound was prepared from L-malic acid according to the method developed by our group (You et al., 2006) and other groups (Borjesson et al., 1992;Dardonville et al., 2003;Gaunt et al., 2003;Saito et al., 1992). Our interest is focused on the changes caused by introducing difluoromethylene group into the lactone ring.
Here we report the crystal structure of the title compound.
The absolute configuration of the title compound was determined by the known chirality of the C8 derived from the starting material, L-malic acid. All bond lengths and angles in the lactone ring are within normal ranges. The dioxolane five-membered ring and the lactone ring both adopt a half-chair conformation. Intermolecular interactions C6-H6···O1 and C8-H6···O1 arrange the moleculesd in a head-to-head fashion (see Fig. 2).

Refinement
All H atoms could be located in a difference Fourier map. The H atoms from the piran-2-one fragment and the methine H8 atom were fully refined. The remaining H atoms were placed in calculated positions (C-H = 0.97-0.98 Å) and refined using a riding model approximation with U iso (H) = 1.2U eq (C) or U iso (H) = 1.5U eq (methyl C). Friedel pairs were merged as no significant anomalous scattering effects were observed. The absolute configuration was related to a known chirality (S) of the dioxolane C8 atom. The high R int value results from a poor quality of the measured crystal. Fig. 1. A view of the molecule of the title compound. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.   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.