6a-Nitro-6-(2,2,7,7-tetramethyltetrahydro-3aH-bis[1,3]dioxolo[4,5-b:4′,5′-d]pyran-5-yl)-6a,6b,7,8,9,11a-hexahydro-6H-spiro[chromeno[3,4-a]pyrrolizine-11,11′-indeno[1,2-b]quinoxaline]

In the title compound, C39H38N4O8, the quinoxaline and indene subunits are essentially planar, with maximum deviations of 0.071 (2) and 0.009 (2) Å, respectively. The indenoquinoxaline system forms a dihedral angle of 72.81 (3)° with the chromenopyrrolizine system. The two dioxolane rings, as well as the pyran ring of the chromeno group and the terminal pyrrolizine, each adopt an envelope conformation with O and C as flap atoms. The central pyrrolizine ring adopts a twisted conformation. Intramolecular C—H⋯O and C—H⋯N hydrogen bonds occur. The crystal structure exhibits C—H⋯O hydrogen bonds, and is further stablized by C—H⋯π interactions, forming a two-dimensional network along the bc plane.

In the title compound, C 39 H 38 N 4 O 8 , the quinoxaline and indene subunits are essentially planar, with maximum deviations of 0.071 (2) and 0.009 (2) Å , respectively. The indenoquinoxaline system forms a dihedral angle of 72.81 (3) with the chromenopyrrolizine system. The two dioxolane rings, as well as the pyran ring of the chromeno group and the terminal pyrrolizine, each adopt an envelope conformation with O and C as flap atoms. The central pyrrolizine ring adopts a twisted conformation. Intramolecular C-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds occur. The crystal structure exhibits C-HÁ Á ÁO hydrogen bonds, and is further stablized by C-HÁ Á Á interactions, forming a two-dimensional network along the bc plane.

Comment
Spiro compounds are a particular class of naturally occurring substances characterized by highly pronounced biological properties (Kobayashi et al., 1991;James et al., 1991). Quinoxaline derivatives are an important class of benzoheterocycles. They have found applications as anticancer, antiviral, and antibacterial agents (Seitz et al., 2002;He et al., 2003).
The structure is stabilized by an intermolecular C-H···O hydrogen bond and additional intramolecular C-H···O and C -H···N hydrogen bonds (Table 1). The crystal structure is further consolidated by C-H ···Cg8 interactions where Cg8 is the centroid of C7\C8\C13\C14\N1\N2 ring.

Refinement
Hydrogen atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 -0.97 Å and U iso (H) = 1.5 U eq (C) for methyl H atoms and 1.2 U eq (C) for other H atoms.

Computing details
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.17 e Å −3 Δρ min = −0.20 e Å −3 Absolute structure: Flack (1983), 2933 Friedel pairs Absolute structure parameter: 0.30 (13) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.