(3aR*,6S*,7S*,7aR*)-2-(4-Methoxybenzyl)-7-(4-nitrophenyl)-6-phenyl-3a,6,7,7a-tetrahydroisoindolin-1-one

The title compound, C28H26N2O4, crystallizes as a racemate with four stereogenic centers. In the molecule, the pyrrolidone ring adopts an envelope conformation and the cyclohexene ring has a twisted envelope conformation. In the crystal structure, molecules are linked by weak intermolecular C—H⋯O hydrogen bonds.

The title compound, C 28 H 26 N 2 O 4 , crystallizes as a racemate with four stereogenic centers. In the molecule, the pyrrolidone ring adopts an envelope conformation and the cyclohexene ring has a twisted envelope conformation. In the crystal structure, molecules are linked by weak intermolecular C-HÁ Á ÁO hydrogen bonds.

Comment
The title compound, C 28 H 26 N 2 O 4 , has a hexahydro-1H-isoindolone core, which is present in both synthetic and naturally occurring bioactive compounds (Walling et al., 1988and Liu et al., 2006, 2008. The title compound has recently been obtained during microwave-assisted intramolecular Diels-Alder cycloaddition along with a minor diastereomer with a 82:18 diastereomeric ratio (Wang et al., 2009;Wu et al., 2006Wu et al., , 2007Wu et al., , 2009. The compound has four stereogenic centers but crystallizes as a racemate as indicated by the centrosymmetric space group. Here we report the crystal structure of the title compound ( Fig. 1).
In the crystal structure of the title compound, there are one pyrrolidone ring and one cyclohexene ring. The pyrrolidone ring C1-C2/C7-C8/N1 adopts envelope conformation, whereas the cyclohexene ring C2-C7 has a twisted envelope conformation. Bond length of C3-C4 is larger than normal C-C single bond because of the hindrance between two phenyl rings at C3 and C4.
The crystal packing (Fig. 2) is stabilized by weak non-classical intermolecular C-H···O hydrogen bonds; the first one between the pyrrolidone H atom and the oxygen of the nitro group, with a C8-H8A···O3 i , and the second one between an H atom of the methoxy group and the oxygen of the C═O unit, with a C28-H28A···O1 ii , respectively (Table 1).

Experimental
To a 10-mL pressurized process vial was added N-(4-methoxybenzyl)-N-(2E,4E)-5-phenylpenta-2,4-dienyl 2-bromoacetamide (133.0 mg, 0.33 mmol), triphenylphosphine (104.0 mg, 0.40 mmol), K 2 CO 3 (68.0 mg, 0.50 mmol), and 4-nitrobenzaldehyde (60.0 mg, 0.40 mmol). After adding aqueous THF (H 2 O:THF = 1:1, 3.5 mL) the loaded vial was then sealed with a cap containing a silicon septum followed by stirring the mixture at room temperature for 6 h to allow the Wittig olefination taking place among the 2-bromoacetamide and the aldehyde. The vial containing the crude Wittig product was then put into the cavity of a technical microwave reactor with the temperature measured by an IR sensor. After heating at 453 K for 0.5 h, the reaction mixture was successively washed with saturated aqueous NH 4 Cl and brine, and then extracted with EtOAc (3 x 5 mL). The combined organic layer was dried over Na 2 SO 4 , filtered, and evaporated under reduced pressure. The residue was purified by flash column chromatography (silica gel, 20% EtOAc in petroleum ether) to furnish the title compound (82.0 mg, 55%), along with a minor diastereomer (17.9 mg, 12%), as a colorless solid. mp 466-468 K (CH 2 Cl 2 -EtOAc-hexane).
Single crystals, as a racemate, suitable for X-ray diffraction of the title compound were grown at ambient temperature in the mixed solvent of methylene chloride, ethyl acetate and hexane (v:v:v = 1:1:3).

Refinement
The H atoms were placed in calculated positions with C-H = 0.93-0.98 Å, and included in the refinement in riding model, with U iso (H) = 1.2U eq (carrier atom). Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at 50% probability level. H atoms are presented as a small spheres of arbitrary radius.

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.
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.