(3S,7aR)-7-Methoxy-7a-methyl-3-phenyl-2,3-dihydropyrrolo[2,1-b]oxazol-5(7aH)-one

In the title chiral butterfly-like bicyclic lactam, C14H15NO3, the phenyl and methyl groups are syn with respect to each other. The dihydropyrrrole ring adopts a boat conformation, whereas the oxazole ring has a slightly distorted boat conformation. The packing of molecules in the crystal structure is stabilized by intermolecular C—H⋯O hydrogen bonds.

In the title chiral butterfly-like bicyclic lactam, C 14 H 15 NO 3 , the phenyl and methyl groups are syn with respect to each other. The dihydropyrrrole ring adopts a boat conformation, whereas the oxazole ring has a slightly distorted boat conformation. The packing of molecules in the crystal structure is stabilized by intermolecular C-HÁ Á ÁO hydrogen bonds.

Comment
The title compound, which was obtained by treating 5-hydroxy-1-((S)-2-hydroxy-1-phenylethyl) -4-methoxy-5-methyl-1Hpyrrol-2(5H)-one and picolinic acid with a catalytic amount of p-TsOH in CH 2 Cl 2 at room temperature, is a key intermediate for the preparation of tetramic acids and methyl tetramates bearing C-5 methyl substituents; this is a key framework in a number of bioactive natural products, such as melophlins and mirabimide E (Huang & Deng, 2004;Huang et al., 2003;Jiang et al., 2009). An X-ray crystal structure determination of the molecular structure of the title compound was carried out to determine its conformation. In the title chiral butterfly-like bicyclic lactam, C 14 H 15 NO 3 , in which the angle O3-C14-C6 is 112.3 (4)°a nd C8-N1-C9 is 119.6 (3)°, the phenyl and methyl groups are syn with respect to each other. The dihydropyrrrole ring adopts a boat conformation, whereas in the oxazole ring the conformation is that of a slightly distorted boat. Bond lengths and angles are in agreement with values reported in the literature (Allen et al., 1987). The packing of molecules in the crystal structure is stabilized by intermolecular C-H···O hydrogen bonds.

Experimental
To a cool (-78 °C) solution of (S)-1-(2-hydroxyl-1-phenylethyl) -3-methoxy-1H-pyrrole-2,5-dione (1.0 mmol) in anhydrous THF (10 ml) was added dropwise CH 3 MgBr (3.0 mmol) in diethyl ether under a nitrogen atmosphere. After stirring at the same temperature for 45 minutes, the reaction was quenched with saturated ammonium chloride (6 ml), and extracted with EtOAc (4 × 10 ml). The combined extracts were washed with brine, dried over Na 2 SO 4 , and concentrated under reduced pressure. The residue was purified by flash chromatography and yielded a mixture of diastereomers. To the mixture of diastereomers (0.51 mmol) in CH 2 Cl 2 (10 ml) was added p-toluenesulfonic acid monohydrate (0.16 mmol.). After stirring for 30 minutes at room temperature, the mixture was quenched with saturated NaHCO 3 solution. The organic layer was separated and the aqueous phase was extracted with CH 2 Cl 2 (3 × 5 ml). The combined organic layers were washed with brine, dried over Na 2 SO 4 , and concentrated under reduced pressure. The residue was purified by flash chromatography to yield the title compound. Single crystals were obtained by slow evaporation of a petroleum ether / ethyl acetate solution.

Refinement
The hydrogen atoms were positioned geometrically, with C-H = 0.93, 0.98, 0.97 and 0.96 Å for phenyl, methine, methylene and methyl H atoms, respectively, and were included in the refinement in the riding model approximation. The displacement parameters of methyl H atoms were set to 1.5U eq (C), while those of other H atoms were set to 1.2U eq (C). In the absence of significant anomalous scattering effects, Friedel pairs were merged.

Special details
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.