Dimethyl trans-3-(4-bromophenyl)-2-methylisoxazolidine-4,5-dicarboxylate

In the title compound, C14H16BrNO5, the isoxazolidine ring adopts an envelope conformation, with the N atom at the flap. In the crystal, intermolecular C—H⋯N and C—H⋯O hydrogen bonds generate R 3 3(18) ring motifs which are fused into a ribbon-like structure extending along the b axis.

In the title compound, C 14 H 16 BrNO 5 , the isoxazolidine ring adopts an envelope conformation, with the N atom at the flap. In the crystal, intermolecular C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds generate R 3 3 (18) ring motifs which are fused into a ribbon-like structure extending along the b axis.

Comment
The 1,3-dipolar cycloaddition of nitrones and alkenes is a powerful synthetic device that allows up to three new stereogenic centers to be assembled in a stereospecific manner in a single step (Confalone & Huie, 1988;Torssell, 1988;Frederickson, 1997;Gothelf & Jorgensen, 1998). Among these N and O containing five-membered heterocycles, isoxazolidines and isoxazoline derivatives have emerged as important candidates and have been shown to display useful anticancer and antiviral properties (Chiacchio et al., 2003).
The syntheses of isoxazolidine derivatives is an important subject in organic chemistry because they are found in the structure of most natural compounds and drugs. In recent years, isoxazolidine derivatives have been synthesized in high yield via intermolecular cycloaddition of N-methylnitrone with disubstituted olefins and are employed for biological evaluation.
These isoxazolidines are used in the syntheses of β-lactams (Padwa et al., 1981) which are of value in the treatment of bacterial infections (Ochiai et al., 1967), occur as natural products (Baldwin & Aube, 1987), serve as versatile synthetic intermediates (Padwa et al., 1984), and are biologically interesting compounds. In view of the interest shown in these compounds, we report herein the crystal structure of the title compound, (I).
The overall view and atom-labelling of the molecule of (I) are displayed in Fig. 1. The isoxazolidine ring (O1/N1/C7-C9) adopts an envelope conformation, with atom N1 displaced by 0.326 (2) Å from the plane of the other ring atoms (Cremer & Pople, 1975).

Refinement
H atoms were positioned geometrically (C-H = 0.93-0.98 Å) and refined using a riding model with U iso (H) = 1.2U eq (C) and 1.5U eq (methyl C). A rotating-group model was used for the methyl groups.