Methyl 4′-benzyl-2,2′-dimethyl-1,3-dioxo-2,3-dihydro-1H,4′H-spiro[isoquinoline-4,5′-oxazole]-4′-carboxylate

In the isoquinoline ring system of the title molecule, C22H20N2O5, the N-heterocyclic ring is in a half-boat conformation. The least-squares plane of the dioxa-2-azaspiro ring [maximum deviation = 0.076 (1) Å] and forms a dihedral angle of 14.54 (4)° with the phenyl ring. In the crystal, molecules are linked via intermolecular C—H⋯O hydrogen bonds into layers parallel to (100).

In the isoquinoline ring system of the title molecule, C 22 H 20 N 2 O 5 , the N-heterocyclic ring is in a half-boat conformation. The least-squares plane of the dioxa-2-azaspiro ring [maximum deviation = 0.076 (1) Å ] and forms a dihedral angle of 14.54 (4) with the phenyl ring. In the crystal, molecules are linked via intermolecular C-HÁ Á ÁO hydrogen bonds into layers parallel to (100).
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Isoquinoline-1,3,4-trione derivatives were reported to be a kind of small molecular inhibitor against caspase-3 which can promote apoptosis of the cells (Du et al., 2008;Chen et al., 2006). They can also attenuate apoptosis of neuronal cells induced by β-amyloid and have been reported to be redox mediators of photosystems I (Mitchell et al., 2000;1995). Spirocyclic oxindoles have emerged as attractive synthetic targets because of their prevalence in numerous natural products and their important biological activity (Galliford & Scheidt, 2007). Among them, the synthesis of spirooxindole oxazoles is of greatest interest (Badillo et al., 2011;Wang et al.;Nair et al., 2002). As a kind of analog of spiroindole oxazolines, spiroisoquinolineoxazolines have rarely been researched. Since a lot of bioactive natural products contain isoquinoline or oxazole rings, it is necessary to develop a methodology to construct such moieties. The title compound, which was derived from isoquinoline-1,3,4-trione and oxazoles (Huang et al., 2011), may has a potential use in biochemical and pharmaceutical fields. Due to the importance of the isoquinoline-1,3,4-trione derivatives, we report in this paper the crystal structure of the title compound.

Experimental
The title compound was the main product from the acid-catalyzed transformation of the photocycloadduct of isoquinoline-1,3,4-trione and 4-benzyl-5-methoxy-2-methyloxazole. The compound was purified by flash column chromatography with ethyl acetate/petroleum ether (1:4 v/v) as eluents. X-ray quality crystals of the title compound were obtained from slow evaporation of an acetone and petroleum ether solution (1:5 v/v). M.p. 451-453 K.

Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 -0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. The highest residual electron density peak and the deepest hole are located at 0.62 and 0.59 Å from C16, respectively. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems 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.