Methyl 4-(4-bromoanilino)-2′,5-dioxo-5H-spiro[furan-2,3′-indoline]-3-carboxylate

In the title compound, C19H13BrN2O5, the spiro furan ring is almost planar with a maximum deviation of 0.034 (2) Å. The indole unit and the furan ring are normal to each other, making a dihedral angle of 87.82 (8) °. The molecular structure is stabilized by an intramolecular N—H⋯O hydrogen bond, which generates an S(6) ring motif. In the crystal, molecules are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers enclosing R 2 2(8) ring motifs.

In the title compound, C 19 H 13 BrN 2 O 5 , the spiro furan ring is almost planar with a maximum deviation of 0.034 (2) Å . The indole unit and the furan ring are normal to each other, making a dihedral angle of 87.82 (8) . The molecular structure is stabilized by an intramolecular N-HÁ Á ÁO hydrogen bond, which generates an S(6) ring motif. In the crystal, molecules are linked via pairs of N-HÁ Á ÁO hydrogen bonds, forming inversion dimers enclosing R 2 2 (8) ring motifs.

Comment
The indole template is generally recognized as an important structure in medicinal chemistry. In particular oxindoles are important constituents of drugs (Akai et al., 2004). The Oxindole motif is present in the anti-Parkinson's drug ropinirole (Gallagher et al., 1985), in non-opioid receptor ligands (Zaveri et al., 2004) and in growth hormone secretagogues (Tokunaga et al., 2001). Tetrahydrofuran is a common motif which can be found in numerous natural products such as polyether antibiotics, nucleosides and lignans (Garzino et al., 2000). The significant difference in length of the C12-O4 = 1.338 (2) Å and C13-O4 = 1.442 (2) Å bonds is attributed to partial contribution from O --C=O + -C resonance structure of the O3═ C12-O4-C13 group (Merlino, 1971). This feature is commonly observed in carboxyl ester groups of the substituents in various compounds where the average distances are 1.340 Å and 1.447 Å, respectively (Varghese et al., 1986). The molecular structure is stabilized by an intramolecular N-H···O hydrogen bond which generates an S(6) ring motif (Table 1).

Experimental
Isatin (1 mmol), p-bromoaniline (1 mmol), and dimethyl acetylene dicarboxylate (DMAD; 1 mmol) were stirred at room temperature in methanol in the presence of Triethylamine (20 mol %) for 4 hrs. The solid formed was filtered and recrystallized from methanol to afford the title compound as a pure yellow solid (85% yield).

Refinement
The hydrogen atoms were located in difference electron density maps. The H-atoms of the amine groups were refined with distance restraints of N-H = 0.89 (2) Å with U iso (H) = 1.2U eq (N). The C bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 and 0.96 Å for CH and CH 3 H atoms, respectively, with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at 30% probability level.

Figure 2
Part of crystal packing of the title compound, showing the formation of the intramolecular S(6) ring motif and the R 2 2 (8)inversion dimer, as viewed along the b-axis [see Table 1 for details of the hydrogen bonding (dashed lines); symmetry code: (i) -x, -y + 1, -z + 2].

sup-3
Acta Cryst. (2014). E70, o210-o211  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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 −0.4990 (