Crystal structure of 3,13-dimethoxy-5,6,10,11-tetrahydrofuro[3,4-i][5]helicene-7,9-dione

In the crystal, the molecules form a layered structure parallel to (10) via C—H⋯O hydrogen-bonding interactions. Adjacent layers are also linked by C—H⋯O hydrogen bonds, forming a three-dimensional structure.


Chemical context
Helicenes are polycyclic aromatic hydrocarbons (PAHs) consisting of ortho-fused aromatic rings arranged in a helical chirality. Among various applications of helicenes (Shen & Chen, 2012;Gingras, 2013), the use of helicene derivatives as light emitters in organic light-emitting diodes has been reported (Sahasithiwat et al., 2010;Shi et al., 2012). The title compound is a derivative of pentahelicene in which two electron-donating groups, i.e. methoxy -OCH 3 , and an electron-withdrawing group, i.e. dicarboxylic anhydride -C(=O)OC(=O)-, are added onto the structure. The arrangement of electron donating and withdrawing groups are set into a Ã-shape with the electron-withdrawing group located in the middle, resulting in an effective push-pull system. Moreover, The two rings connected to the central benzene ring are non-aromatic and are in a twist conformation.

Supramolecular features
In the crystal structure, C-HÁ Á ÁO hydrogen-bonding interactions (Table 1) between B molecules leads to a formation of a molecule B layer (Fig. 2), while C-HÁ Á ÁO hydrogenbonding interactions involving A molecules leads to the formation of a molecule A layer (Fig. 3). The two layers are positioned alternately parallel to (101), as displayed in Fig. 4. Adjacent layers are connected by further C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional structure.

Figure 2
Part of the crystal structure, projected along the a axis, depicting a layer consisting of B molecules linked through hydrogen bonds (blue dashed lines) and connecting to A molecules by further hydrogen bonds. The carbon atoms of molecules A (green) and B (dark gray) are colored differently.
reaction mixture was allowed to cool to room temperature, filtered, and the solid was washed with dichloromethane (600 ml). The solvents were removed from the filtrate under reduce pressure to gain the crude product, which was further purified by column chromatography (silica gel, ethyl acetatehexane) to give the title compound (18.3g, 60%) as a yellow solid, which was characterized by FTIR, 1 H-NMR and 13 C-NMR. Crystals suitable for X-ray analysis were obtained by slow vapor diffusion of hexane into a solution of the title compound in chloroform.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were placed in calculated positions and treated as riding atoms with C-H = 0.93-0.97 Å and with U iso = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.

Figure 3
Part of the crystal structure, projected along the a axis, depicting a layer consisting of A molecules linked through hydrogen bonds (blue dashed lines) and connecting to B molecules by further hydrogen bonds. The carbon atoms of molecules A (green) and B (dark gray) are colored differently.