(1S,3aS,4S,7aS)-Ethyl 1-benzyl-2-(4-methoxybenzyl)-6,7-dimethyl-3-oxo-2,3,3a,4,5,7a-hexahydro-1H-isoindole-4-carboxylate dichloromethane monosolvate

In the title compound, C28H33NO4·CH2Cl2, the pyrrolidone ring adopts a twisted envelope conformation and the cyclohexene has a half-chair conformation. In the crystal, weak C—H⋯O hydrogen bonds link the components into chains along [100].


Comment
The scaffold of isoindolin-1-ones have derived many natural products and have great research values, such as cytochalasins (Liu et al. , 2006;Cox et al., 1983). In our total synthesis of cytochalasin Z 8 , we have obtained the title compound as a major product through intramolecular Diels-Alder reaction. The structure of the title compound has been characterized by spectroscopic methods and further confirmation by X-ray analysis. The molecule has four rings including two benzene rings and one pyrrolidone ring and one cyclohexene ring and has four stereogenic centers as indicated absolute stereoconfiguration. We report here its crystal structure (Fig. 1). In the crystals of the title compound, the pyrrolidone ring C9/C17-C19/N1 adopts twisted envelope conformation, whereas the cyclohexene ring C17-C18/C20-C23 has a half chair conformation. The crystal packing (Fig. 2) is stabilized by two weak non-classical intermolecular C-H···O hydrogen bonds, the first one between H atom of dichloromethane and the carbonyl oxygen of the pyrrolidone, with a C29-H29B···O2 i , and the second one between the H atom on the benzene ring of methoxybenzyl group and the carbonyl oxygen of the carboxylate group, with C6-H6···O3 ii , respectively (Table 1).
Single crystals suitable for X-ray diffraction of the title compound were grown in CH 2 Cl 2 .

Refinement
The H atoms were placed in calculated positions with C-H = 0.93-0.98 Å according to their own hybridization model.
And included in the refinement in riding model with U iso (H)=1.2U eq or 1.5U eq (sp 3 ) of the carrier atom.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. (1S,3aS,4S,7aS)-Ethyl 1-benzyl-2-(4-methoxybenzyl)-6,7-dimethyl-3-oxo-2,3,3a,4,5,7a-hexahydro-1H-  (11) 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 > 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.