4-[(2,4-Dimethyl-1,3-oxazol-5-yl)methyl]-4-hydroxy-2-methylisoquinoline-1,3(2H,4H)-dione

In the title isoquinolinedione derivative, C16H16N2O4, the piperidine ring in the tetrahydroisoquinoline unit adopts a half-boat conformation. The essentially planar oxazole ring [maximum deviation = 0.004 (2) Å] is inclined at a dihedral angle of 36.00 (8)° to the tetrahydroisoquinoline unit. In the crystal structure, pairs of intermolecular C—H⋯O and O—H⋯N interactions link the molecules into chains incorporating R 2 2(9) ring motifs. Two neighbouring chains are further interconnected by intermolecular C—H⋯O interactions into chains two molecules wide along the a axis.

In the title isoquinolinedione derivative, C 16 H 16 N 2 O 4 , the piperidine ring in the tetrahydroisoquinoline unit adopts a half-boat conformation. The essentially planar oxazole ring [maximum deviation = 0.004 (2) Å ] is inclined at a dihedral angle of 36.00 (8) to the tetrahydroisoquinoline unit. In the crystal structure, pairs of intermolecular C-HÁ Á ÁO and O-HÁ Á ÁN interactions link the molecules into chains incorporating R 2 2 (9) ring motifs. Two neighbouring chains are further interconnected by intermolecular C-HÁ Á ÁO interactions into chains two molecules wide along the a axis.

Experimental
The title compound was obtained in the reaction between 1,3,4(2H)-isoquinolinetrione and 2,4,5-trimethyloxazole. The compound was purified by flash column chromatography in ethyl acetate and petroleum ether. X-ray quality single crystals of the title compound were obtained from slow evaporation of a chloroform solution. M.p. 434-436 K.

Refinement
All the H atoms were located from difference Fourier map [range of C-H = 0.91 (2) -1.01 (3) Å] and allowed to refine freely.

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.