Methyl 4′-isobutyl-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, C19H22N2O5, the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-azaspiro ring is essentially planar [maximum deviation = 0.042 (1) Å] and forms a dihedral angle of 81.85 (4)° with the benzene ring. In the crystal, the molecules are linked via intermolecular C—H⋯O hydrogen bonds into chains along [010].

In the isoquinoline ring system of the title molecule, C 19 H 22 N 2 O 5 , the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-azaspiro ring is essentially planar [maximum deviation = 0.042 (1) Å ] and forms a dihedral angle of 81.85 (4) with the benzene ring. In the crystal, the molecules are linked via intermolecular C-HÁ Á ÁO hydrogen bonds into chains along [010].
Oxazole rings are also found in some bioactive natural products such as Annuloline and Ostreogrycin A. Spirooxazoles have emerged as attractive synthetic targets because of their potent bioactivity (Badillo et al., 2011;Wang et al.;Nair et al., 2002). 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 with a relative configuration of (4S * , 4'S * ).

Experimental
The title compound was the main product from the acid-catalyzed transformation of the photocycloadduct of isoquinoline-1,3,4-trione and 4-isobutyl-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/petroleum ether solution (1:5 v/v). M.p. 421-423 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 is located at 0.75 Å from C17 and the deepest hole is located at 0.53 Å from C11. 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.