Crystal structure and Hirshfeld surface analysis of ethyl 2-[9-(2-hydroxyphenyl)-3,3,6,6-tetramethyl-1,8-dioxo-2,3,4,4a,5,6,7,8a,9,9a,10,10a-dodecahydroacridin-10-yl]acetate

The molecular conformation is stabilized by an intramolecular O—H⋯O hydrogen bond between the hydroxy substituent on the benzene ring and one of the carbonyl groups of the acridinedione unit.

In the title compound, C 27 H 33 NO 5 , a 3,3,6,6-tetramethyltetrahydroacridine-1,8dione ring system carries an ethyl acetate substituent on the acridine N atom and an o-hydroxyphenyl ring on the central methine C atom of the dihydropyridine ring. The benzene ring is inclined to the acridine ring system at an angle of 80.45 (7) and this conformation is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond between the hydroxy substituent on the benzene ring and one of the carbonyl groups of the acridinedione unit. The ester C O oxygen atom is disordered over major and minor orientations in a 0.777 (9):0.223 (9) ratio and the terminal -CH 3 unit of the ethyl side chain is disordered over two sets of sites in a 0.725 (5): 0.275 (5) ratio. In the crystal, C-HÁ Á ÁO hydrogen bonds combine to link the molecules into a three-dimensional network. van der Waals HÁ Á ÁH contacts contribute the most to the Hirshfeld surface (66.9%) followed by OÁ Á ÁH/HÁ Á ÁO (22.1%) contacts associated with weak hydrogen bonds.

Chemical context
Acridine derivatives occur in a number of compounds of importance in medicinal chemistry such as bucricaine, which used for surface anesthesia of the eye and given by injection for infiltration anesthesia, peripheral nerve block and spinal anesthesia (Ramesh et al., 2012). Quinacrine, also known as mepacrine, is used as a gametocytocide and acts as an antimalarial agent (Valdé s, 2011). Proflavin is also found to be active as a bacteriostatic agent (Patel et al., 2010) and nitracrine is as anticancer agent (Cholewinski et al., 2011). Acriflavin is used as an antiseptic for skin and mucous membranes (Ramesh et al., 2012). As part of our studies in this area, we report herein the synthesis and crystal structure of the title compound, C 27 H 33 NO 5 .

Structural commentary
As shown in Fig.1, the 3,3,6,6-tetramethyltetrahydroacridine-1,8-dione ring system carries an ethyl acetate substituent on the acridine N1 atom and an o-hydroxyphenyl ring on the central methine C7 atom of the C1/C6-C8/C13/N1 dihydropyridine ring. The acridinedione ring system deviates signifi- ISSN 2056-9890 cantly from planarity with an r.m.s. deviation of 0.404 Å for the thirteen C atoms and one N atom of the acridine unit. The benzene ring is inclined to the acridine ring system at a dihedral angle of 80.45 (7) .
The outer C1-C6 and C8-C13 cyclohexenone rings both adopt flattened chair conformations with the C4 and C11 atoms displaced in the same direction, by 0.308 (2) and 0.338 (2) Å , respectively, from the best-fit planes through the remaining five C atoms. In contrast, the central C13/N1/C1/ C6-C8 ring can best be described as a flattened boat with N1 and C7 displaced by 0.146 (1) and 0.191 (14) Å , respectively, from the remaining four C atoms. The bond lengths and angles in the title molecule agree reasonably well with those found in closely related molecules (Abdelhamid et al., , 2014Khalilov et al., 2011).
The molecular conformation of the title compound is stabilized by an intramolecular O5-H5Á Á ÁO1 hydrogen bond between the hydroxy substituent on the benzene ring and one of the carbonyl groups of the acridinedione unit (Table 1; Fig. 1). Atom O3 is disordered over major and minor orientations in a 0.777 (9):0.223 (9) ratio and the terminal C17 methyl group is disordered over two sets of sites in a 0.725 (5):0.275 (5) ratio.

Supramolecular features
In the crystal, a number of C-HÁ Á ÁO hydrogen bonds link the molecules into a three-dimensional network (Table 1; Fig. 2); all the oxygen atoms in the molecule except O4 accept at least one of these bonds.

Hirshfeld surface analysis
The CrystalExplorer software (Wolff et al., 2012) was used to produce the d norm -mapped Hirshfeld surfaces and the electrostatic potential for the title compound. The contact distances, d i and d e , from the Hirshfeld surface to the nearest atom, inside and outside, respectively, enable the analysis of the intermolecular interactions through the mapping of d norm .

Figure 2
The molecular packing, viewed down the a-axis direction, showing hydrogen bonds as dashed lines.

Figure 1
The title molecule with displacement ellipsoids drawn at the 30% probability level. Only the major disorder components for O3 and C17 are shown.
An illustration of the inter-molecular contacts in the crystal is given by two-dimensional fingerprint plots.
The bright-red spots on the Hirshfeld surface mapped over d norm (Fig. 3), with labels H27B, H12B, H14A, H14B, H2A and H2B on the surface represent donors for potential C-HÁ Á ÁO hydrogen bonds (see Table 1); the corresponding acceptors on the surface appear as bright-red spots at atoms O1, O2 and O5. Short HÁ Á ÁH contacts are given in Table 2.
The DABSAD compound crystallizes with two molecules in the asymmetric unit. In each molecule, the central 1,4-dihydropyridine ring adopts a shallow sofa conformation (with the C atom bearing the phenol ring as the flap), whereas the pendant cyclohexene rings both have twisted-boat conformations. Each molecule features an intramolecular O-HÁ Á ÁO hydrogen bond, which closes an S(8) ring. In the crystal, the molecules are linked by O-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á Á interactions, forming a three-dimensional network. In VANBUK, the central 1,4-dihydropyridine ring adopts a shallow sofa conformation (with the C atom bearing the bromophenol ring as the flap), whereas the pendant cyclohexene rings both have twisted-boat conformations. The molecule features an intramolecular O-HÁ Á ÁO hydrogen bond, which closes an S(8) ring. In the crystal, molecules are linked by C-HÁ Á ÁO interactions, forming C(12) chains propagating along the c-axis direction. In the crystal of    A view of the three-dimensional Hirshfeld surface for the title compound, plotted over d norm in the range À0.14 to 1.68 a.u.
SILBIB, O-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á Á(ring) hydrogen bonds combine with an Br-O and unusual C-BrÁ Á Á(ring) halogen bonds to generate a three dimensional network with molecules stacked along the a-axis direction. In the acridinedione moiety of PUSJEU, the central dihydropyridine ring adopts a flattened-boat conformation, with the N atom and the methine C atom displaced from the mean plane of the other four atoms by 0.0513 (14) and 0.1828 (18) Å , respectively. The two cyclohexenone rings adopt envelope conformations, with the tetrasubsituted C atoms as the flap atoms. In the crystal, molecules are linked via a pair of C-HÁ Á ÁO hydrogen bonds, forming inversion dimers, which are, in turn, linked by C-HÁ Á ÁO hydrogen bonds, forming slabs lying parallel to (001).

Synthesis and crystallization
To a mixture of dimedone (1.12 g, 0.008 mol), ethyl glycinate hydrochloride (0.56 g, 0.004 mol) and salicaldehyde (0.43 ml, 0.004 mol) in ethanol (20 ml), triethyl amine (1.12 ml, 0.008 mol) was added. The reaction mixture was heated under reflux for 5 h at 353-358 K then left to cool. The separated solid was filtered off, dried and recrystallized from ethanol solution as yellow plates of the title compound, yield 68%, m.p. 497 K.