(1S*,2R*,3S*,4R*,5R*)-5-Tetradecyloxymethyl-7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride

In the title compound, C23H38O5, the oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride unit has a normal geometry and the tetradecoxymethyl side chain is fully extended. In the crystal, molecules are linked head-to-head by C—H⋯O hydrogen bonds, forming two-dimensional networks propagating along the a and c-axis directions.

In the title compound, C 23 H 38 O 5 , the oxabicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride unit has a normal geometry and the tetradecoxymethyl side chain is fully extended. In the crystal, molecules are linked head-to-head by C-HÁ Á ÁO hydrogen bonds, forming two-dimensional networks propagating along the a and c-axis directions.

Forbes Comment
The pericyclic [4 + 2] cycloaddition can arguably be considered as one of the most versatile transformations when considering both atom economy and stereochemistry as reported by Oppolzer (1991), Pindur et al. (1993), and Pellissier (2012. When coupled to processes which are driven under kinetic or thermodynamic reaction conditions as illustrated by Lowry & Richardson (1987) and Smith (2012), the opportunity to illustrate both modalities on one unified system exists.
That is, the irreversible hydrogenation of alkenes as reported by Brieger & Nestrick (1974) and Knowles (2002) and the reversible [4 + 2] cycloaddition when using not cyclopentadiene but furan with maleic anhydride as reported by Palmer (2004) provided us with a platform to illustrate both processes on one system. Upon reversible cycloaddition of a substituted furan with maleic anhydride, the resulting alkene was subjected to catalytic hydrogenation of the alkene.
As the end product was both crystalline and suitable for X-ray analysis, we succeeded in illustrating both reaction pathways of kinetic and thermodynamic driven processes through the establishment of five contiguous stereocenters, as shown in Fig. 1.
The title compound was isolated as the major product in moderate yield and offered definitive evidence of the facial selectivity involved in the catalytic hydrogenation as well as the juxtaposition of the anhydride relative to the bicyclic scaffold as a result of the [4 + 2] cycloaddition. The configurations of the preexisting sites C1, C2, C3, and C4 prior to the hydrogenation of the alkene are S, R, S, and R for one of the enantiomers of the racemic mixture, and R, S, R, and S for the other, respectively. The configuration of the newly formed stereocenter upon hydrogenation of the chiral racemic mixture is R for the former, S for the latter, which confirms a profile of kinetic reaction control for the hydrogenation and thermodynamic reaction control for the cycloaddition.
In the solid state structure of the title compound ( Fig. 1) the small amount of vibrational motion of the tetradecoxymethyl tail group indicates a significant degree of non-covalent interactions within those domains. No unusual deviations from normal bond distances or bond angles are observed in the title molecule.
In the crystal, molecules are linked head-to-head via C-H···O hydrogen bonds (Table 1) to form V-shaped or folded twodimensional networks extending in the a and c directions. In the crystal, there are clear hydrophobic and hydrophilic domains (Fig. 2).
The title compound was prepared by bubbling hydrogen gas into a tetrahydrofuran (50 ml) solution consisting of the Diels-Alder adduct starting material (607 mg, 1.5 mmol) and 10% Pd/C (64 mg) for a period of no less than 90 min. at room temperature. The reaction mixture was then filtered through a plug of Celite and concentrated under reduced pressure. Purification by column chromatography (EtOAc/hexanes, 1/4) afforded the title compound (154 mg, 26% yield). Colourless plate-like crystals were obtained on slow evaporation of a solution in the solvent mixture EtOAc/hexanes (1/4). Spectroscopic data for the title compound are available in the archived CIF.

Refinement
H atoms were placed in calculated positions and treated as riding atoms: C-H = 0.98, 0.99 and 0.100 Å for CH 3 , CH 2 and CH H atoms, respectively, with U iso (H) = k × U eq (C) where k = 1.5 for CH 3 H atoms, and = 1.2 for other H atoms.    Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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 > 2sigma(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.