rac-Methyl 4-azido-3-hydroxy-3-(2-nitrophenyl)butanoate

In the title compound, C11H12N4O5, the mean plane through the nitro substituent on the benzene ring is inclined to the benzene mean plane by 85.8 (2)°, which avoids steric interactions with the ortho substituents. The hydroxy group is involved in bifurcated hydrogen bonds. The first is an intramolecular O—H⋯O hydrogen bond, involving the ester carbonyl O atom, which gives rise to the formation of a boat-like hydrogen-bonded chelate ring. The second is an intermolecular O—H⋯N hydrogen bond involving the first N atom of the azide group of a symmetry-related molecule. In the crystal structure this leads to the formation of a polmer chain extending in the c-axis direction.

In the title compound, C 11 H 12 N 4 O 5 , the mean plane through the nitro substituent on the benzene ring is inclined to the benzene mean plane by 85.8 (2) , which avoids steric interactions with the ortho substituents. The hydroxy group is involved in bifurcated hydrogen bonds. The first is an intramolecular O-HÁ Á ÁO hydrogen bond, involving the ester carbonyl O atom, which gives rise to the formation of a boatlike hydrogen-bonded chelate ring. The second is an intermolecular O-HÁ Á ÁN hydrogen bond involving the first N atom of the azide group of a symmetry-related molecule. In the crystal structure this leads to the formation of a polmer chain extending in the c-axis direction.
In the synthesis of Rhazinilam analogues developed in our group the Mukaiyama reaction, a versatile synthetic tool in organic chemistry, is a key step reaction (Mukaiyama et al., 1974). In one of our retrosynthetic approaches (1methoxyvinyloxy)trimethysilane was used as a nucleophile, 2-azido-1-(2-nitrophenyl)ethanone as an electrophile and TiCl 4 as a Lewis acid, to synthesize the title hydroxyester, in high yield. This hydroxyester is a suitable precursor for the formation of the pyrrolinone required for the next step in the synthesis of Rhazinilam analogues (Vallat, 2004;Vallat et al., 2009).
The molecular structure of the title compound is illustrated in Fig. 1. The bond distances and angles are normal. The mean plane through the nitro group is inclined to the benzene mean plane by 85.8 (2)°, so avoiding steric interactions with the ortho substituents. The hydroxyl group (O3) is involved in bifurcated hydrogen bonds (Table 1) (Table 1). This leads to the formation of a polymer chain extending in the c direction. (Fig. 2). There are also two weak intermolecular C-H···O interactions involving atoms O1 and O4 and the hydrogen atoms of the butanoate moiety (Table 1).

Experimental
Under an atmosphere of Ar, (1-methoxyvinyloxy)trimethylsilane (1.06 g, 7.3 mmol) was dissolved in dry CH 2 Cl 2 (15 ml) and the temperature lowered to 243K. 2-Azido-1-(2-nitrophenyl)ethanone (0.5 g, 2.4 mmol) dissolved in dry CH 2 Cl 2 (6 ml) was added to the reaction mixture dropwise. A solution of TiCl 4 (0.13 ml, 1.2 mmol), freshly distilled over polyvinylpyridine, in dry CH 2 Cl 2 (4 ml), was added slowly. The solution became immediately red and then dark red. The reaction mixture was stirred at 243K for 15 min and then at 258K for 30 min. The cold mixture was then poured into an aqueous solution of 2 N NaOH (2.4 ml) and extracted with chloroform. The combined organic layers were washed with brine, dried over   Table 1 for details).

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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 > σ(F 2 ) is used only for calculating Rfactors(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.