6-Benzyl-3-(1,4-dioxaspiro[4.5]decan-2-yl)-8,8-dimethyl-1-oxa-2,6-diazaspiro[4.4]non-2-ene-7,9-dione

In the title compound, C23H28N2O5, the 4,5-dihydroisoxazole ring adopts a slight envelope conformation and the dioxolane ring is in a twisted conformation. The molecular structure, in the vicinity of the benzyl group, may be influenced by an intramolecular C—H⋯O hydrogen bond which generates an S(7) ring motif. In the crystal structure, molecules are linked via weak intermolecular C—H⋯O hydrogen bonds, forming extended chains along the b axis. Further stabilization is provided by weak C—H⋯π interactions.

In the title compound, C 23 H 28 N 2 O 5 , the 4,5-dihydroisoxazole ring adopts a slight envelope conformation and the dioxolane ring is in a twisted conformation. The molecular structure, in the vicinity of the benzyl group, may be influenced by an intramolecular C-HÁ Á ÁO hydrogen bond which generates an S(7) ring motif. In the crystal structure, molecules are linked via weak intermolecular C-HÁ Á ÁO hydrogen bonds, forming extended chains along the b axis. Further stabilization is provided by weak C-HÁ Á Á interactions.

Comment
Natural products containing pyrrolidinone carbon skeletons continue to attract the interest of chemists and biologists due to their challenging structures and remarkable biological properties (Iida et al., 1986;Matkhalikova et al., 1969;Reddy & Rao, 2006;Reiner, 2007;Royles, 1996). Amongst these, polychlorinated pyrrolidinone i.e. dysidamide analogues extracted from the marine sponge, Lamellodysidea herbacea, display remarkable biological activities (Sauleau & Bourguet-Kondracki, 2005). We have synthesized the title compound, which may act as an essential intermediate in the synthesis of dysidamide and its crystal structure is reported herein.
In the solid state ( Fig. 2), the molecules are linked via intermolecular C14-H14A···O1 i hydrogen bonds to form onedimensional chains along the b-axis and are further consolidated by C-H···π (Table 1)

interactions.
Experimental 935 mg (4.25 mmol) of the hydroximoyl chloride at 273 K was dissolved in 100 ml of diethyl ether and 650 mg (2.84 mmol) of N-protected-5-methylene-pyrrolidine-2,4-dione was added. To this mixture 9.35 ml (0.5 M, 4.675 mmol) of triethylamine solution in ether was added dropwise at a rate of 8 to 10 drops/min over 4h and stirred overnight. The mixture was then quenched by addition of 100ml HCl (2 N) and partitioned against ether (4 x 60 ml). The combined organic phases were washed with NaHCO 3 (100 ml) and water (2 x 100 ml), then dried with MgSO 4 , and concentrated in vacuo (15 mbar) to give a yellow oil. Crystallization from diethyl ether gave the analytically and spectroscopically pure spiroisoxazoline (880 mg, 75 %) as colourless crystals. M.p. 403-404 K.

Refinement
All H atoms were placed in the calculated positions, with C-H = 0.93-0.98 Å, and refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. In the absence of significant anomalous dispersion, 3651 Friedel pairs were merged for the final refinement.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.