Methyl 12-hydroxy-10-[1-(4-methoxyphenyl)-2-oxo-3-phenoxyazetidin-4-yl]-11-oxa-3-azahexacyclo[11.7.1.02,9.02,12.03,7.017,21]henicosa-1(20),13,15,17(21),18-pentaene-9-carboxylate

In the title compound, C37H34N2O7, both pyrrolidine rings adopt envelope conformations. The β-lactam ring is close to planar (r.m.s. deviation = 0.0395 Å) and makes a dihedral angle of 83.35 (15)° with the furan ring. The O atom attached to the β-lactam ring deviates by 0.187 (2) Å from the mean plane of the ring. The β-lactam ring makes dihedral angles of 14.90 (15) and 27.72 (17)° with the methoxyphenyl and phenyl rings, respectively. The crystal packing features C—H⋯O hydrogen bonds.

In the title compound, C 37 H 34 N 2 O 7 , both pyrrolidine rings adopt envelope conformations. The -lactam ring is close to planar (r.m.s. deviation = 0.0395 Å ) and makes a dihedral angle of 83.35 (15) with the furan ring. The O atom attached to the -lactam ring deviates by 0.187 (2) Å from the mean plane of the ring. The -lactam ring makes dihedral angles of 14.90 (15) and 27.72 (17) with the methoxyphenyl and phenyl rings, respectively. The crystal packing features C-HÁ Á ÁO hydrogen bonds.

Experimental
A solution of methyl 2-(hydroxy(1-(4-methoxyphenyl)-4-oxo-3-phenoxyazetidin -2-yl)methyl)acrylate (1.0 equiv.), acenaphthequinone (1.1 equiv.) and proline (1.1 equiv.) were refluxed in dry methanol. Completion of the reaction was evidenced by TLC analysis. The solvent was then removed under vacuum, diluted in dichloromethane and washed with brine and water. The organic layer was separated and removed and the residue subjected to column chromatography using ethyl acetate and hexane as an eluent (1:4) afforded the cycloadduct. The product was dissolved in chloroform and heated for two minutes. The resulting solution was subjected to crystallization by slow evaporation of the solvent for 48 hours resulting in the formation of single crystals.

Refinement
The hydrogen atoms were placed in calculated positions with C-H = 0.93 Å to 0.98 Å and refined in the riding model with fixed isotropic displacement parameters:U iso (H) = 1.5U eq (methyl-C) and 1.2U eq (non-methyl C). The hydroxyl Hatom was located from a difference map and was allowed to refine freely.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms were omitted for clarity.  H atoms non-participating in hydrogen-bonding were omitted for clarity.

Methyl 12-hydroxy-10-[1-(4-methoxyphenyl)-2-oxo-3-phenoxyazetidin-4-yl]-11-oxa
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq