(1S*,4′S*,5R*)-1-Isobutyl-5-methoxy-2′,3-dimethyl-4,6-dioxa-2-azaspiro[bicyclo[3.2.0]hept-2-ene-7,4′-isoquinoline]-1′,3′(2′H,4′H)-dione

In the isoquinoline ring system of the title compound, C19H22N2O5, the N-heterocyclic ring is in a half-chair conformation. The dioxa-2-azaspiro ring is essentially planar [maximum deviation of 0.025 (1) Å] and forms a dihedral angle of 23.51 (5)° with the benzene ring. In the crystal, molecules are linked via weak intermolecular C—H⋯O and C—H⋯N hydrogen bonds into chains along [010].


Comment
Oxazole rings are found in some bioactive natural products such as Annuloline and Ostreogrycin A. Compounds with oxazole moiety have been found to have inhibition activity on malignant tumors (Harris et al., 2005). Additionally, many natural products especially the alkaloids containing the isoquinoline or oxazole ring are bioactive. As such there has been intense development of methodology to construct such moieties (Wang et al., 2010). Isoquinolines are often found in bioactive natural products. They have been used to build blocks of benzo[c]phenanthridine alkaloids (Pollers-Wieers et al., 1981;Malamas et al., 1994;Yu et al., 2010). 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. . Isoquinoline-1,3,4-trione and its derivatives have been reported to be redox mediators of photosystems I and have been used as herbicides (Mitchell et al., 2000;1995).
The title compound which was derived from isoquinoline-1,3,4-trione and oxazoles  may have potential use in biochemical and pharmaceutical fields. We report herein the crystal structure of the title compound with a relative configuration of (1S * , 4'S * , 5R * ).

Experimental
The title compound was the main product from the photoreaction between 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) as eluents. X-ray quality crystals of the title compound was obtained from slow evaporation of an acetone and petroleum ether solution of the title compund (1:5) (m.p. 421-423 K).
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 -0.98 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. 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.