2,5,11,14-Tetraoxa-8-azadispiro[13.4.0]nonadeca-15,17,19-triene

The title compound, C14H21NO4, has been synthesized from o-dihydroxybenzene by a three-step reaction. There are two chemically equal but crystallographically independent molecules in the asymmetric unit. The crystal packing is governed by C—H⋯O hydrogen bonds and C—H⋯π interactions, forming an infinite network.

In the title molecule ( Fig. 1), bond lengths and angles are within normal ranges (Allen et al., 1987). There are two chemically equal but crystallographically independent molecules per asymmetric unit.

Experimental
The title compound was prepared according the previous literature. The product was isolated, recrystallized from ethyl acetate, and then dried in vacuum to give the pure title compound in 63% yield. The single crystals suitable for X-ray analysis were obtained as colourless blocks by slow evaporation of an ethyl acetate solution.

Refinement
Due to insignificant anomalous dispersion effects, Friedel pairs were merged before refinement.
The H atoms were included in calculated positions and refined using a riding model approximation. Constrained C-H and N-H bond lengths and isotropic U parameters: 0.93 Å and U iso (H) = 1.2U eq (C) for Csp 2 -H; 0.97 Å and U iso (H) = 1.2U eq (C) for methylene C-H; 0.89 Å and U iso (H) = 1.2U eq (N) for imino N-H. Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms.

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 > 2σ(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.