Methyl 2,2′-dimethyl-4′-[2-(methylsulfanyl)ethyl]-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, C18H20N2O5S, the fused N-heterocyclic ring is distorted towards a half-boat conformation. The methyl formate moiety is disordered over two sets of sites with refined occupancies of 0.882 (5) and 0.118 (5). In the crystal, molecules are linked via weak intermolecular C—H⋯O hydrogen bonds into one-dimensional chains along [010].

In the isoquinoline ring system of the title molecule, C 18 H 20 N 2 O 5 S, the fused N-heterocyclic ring is distorted towards a half-boat conformation. The methyl formate moiety is disordered over two sets of sites with refined occupancies of 0.882 (5) and 0.118 (5). In the crystal, molecules are linked via weak intermolecular C-HÁ Á ÁO hydrogen bonds into onedimensional chains along [010].

Comment
Photocycloaddition of isoquinoline-1,3,4-trione combined with following transformation of the photocycloadducts has become facile method to build various scaffold containing isoquinoline moiety (Yu et al., 2010;Huang et al., 2011). Oxazoles can be used to inhibit the activity of malignant tumors (Harris et al., 2005). Spirocyclic oxindoles have emerged as attractive synthetic targets because of their prevalence in numerous natural products and important biological activity (Badillo et al., 2010;Vintonyak et al., 2010). Among them, the synthesis of spirooxindole oxazoles is of great intrest (Badillo et al., 2011;Wang et al., 2010;Nair et al., 2002). Many bioactive natural products especially alkaloids contain an isoquinoline or oxazole ring. It is necessary to develop methodologies to construct such moieties. The title compound which was derived from isoquinoline-1,3,4-trione and an oxazole and may have potential use in biochemical and pharmaceutical fields.

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). The highest residual electron density peak is located at 0.76 Å from C2 and the deepest hole is located at 0.70 Å from S1. The same U ij parameters were used for atom pair C15B/C16B. The methyl formate moiety (O4/O5/C15/C16) is disordered over two positions with refined site-occupancies of 0.882 (5) : 0.118 (5). All minor disordered components were refined isotropically.

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.