Spiro[1,3-dioxolane-2,3′-indolin]-2′-one

The title compound, C10H9NO3, was synthesized by the condensation reaction of isatin (systematic name 1H-indole-2,3-dione) with glycol in presence of p-toluenesulfonic acid. The indol-2-one ring system is essentially planar [N—C—C—C torsion angle = 3.1 (2)°], and the 1,3-dioxolane ring is slightly distorted. The crystal structure exhibits intermolecular N—H⋯O hydrogen bonds.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LX2143).

Comment
Isatin derivatives, has caught great attention of many researchers as a versatile lead molecule for designing of potential drugs for the variety of biological activities, such as anti-bacteria, anti-virus, anti-tumor and neuroprotection. Among these compounds, spiro-oxindol analogues have received considerable attention as potential anti-bacteria and neuroprotection agents (Demosthenes et al. 1998;Rajopadhye et al. 1988;Santos et al. 2008).
The X-ray structural analysis confirmed the assignment of its structure from spectroscopic data. The molecular structure is depicted in Fig. 1, and a diagram of interactions between the title compounds is depicted in Fig. 2. Geometric parameters of the title compound are in the usual ranges. The crystal packing ( Fig. 2) is stabilized by intermolecular N-H···O hydrogen bonds between the indoline H atom and the oxygen of the C═O unit, with a N1-H1···O1 i (Table 1).

Experimental
Isatin (1 mmol) and glycol (1 mmol) was dissolved in cyclohexane (20 ml), and 0.01 mmol TsOH was added. The mixture was stirred under reflux. After completion of the reaction, it was evaporated to dryness, followed by chromatography to the

Refinement
The H atom bound N atom was located from difference Fourier map and refined freely. All H atoms of C atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for aryl and 0.97 Å for methylene H atoms.
U iso (H)= 1.2U eq (C) for all H atoms. Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are presented as a small cycles of arbitrary radius. 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.