2,2,7,7-Tetramethyl-1,2,3,4,5,6,7,8-octahydroacridine-1,8-dione

The whole molecule of the title compound, C17H21NO2, is generated by twofold rotational symmetry. The N atom and the C and H atoms in position 4 of the pyridine ring lie on the twofold axis. The cyclohexene ring has a sofa conformation with the CH2 C atom adjacent to the dimethyl-substituted C atom displaced by 0.5949 (16) Å from the mean plane of the other five C atoms. In the crystal, weak C—H⋯O interactions link the molecules into chains parallel to the a axis. In addition, π–π stacking interactions [centroid–centroid distance = 3.8444 (7) Å] contribute to the stabilization of the crystal structure.

The whole molecule of the title compound, C 17 H 21 NO 2 , is generated by twofold rotational symmetry. The N atom and the C and H atoms in position 4 of the pyridine ring lie on the twofold axis. The cyclohexene ring has a sofa conformation with the CH 2 C atom adjacent to the dimethyl-substituted C atom displaced by 0.5949 (16) Å from the mean plane of the other five C atoms. In the crystal, weak C-HÁ Á ÁO interactions link the molecules into chains parallel to the a axis. In addition,stacking interactions [centroid-centroid distance = 3.8444 (7) Å ] contribute to the stabilization of the crystal structure.

Related literature
For background to potassium channels and biological functions and physiological roles, see: Horiuchi et al. (2001); Crestanello et al. (2000).  Cremer & Pople (1975). For a description of the Cambridge Structural Database, see: Allen (2002). For hydrogen-bond motifs, see: Bernstein et al. (1995).   Table 1 Hydrogen-bond geometry (Å , ). openers, which open vascular potassium channels, have the potential to restrain or prevent contractile responses to excitatory stimuli or clamp the vessel in a relaxed condition. Their vasorelaxant effect is due to an increase in the potassium efflux through opening plasmalemmal potassium channels, which reduce calcium release from intracellular sources (Horiuchi et al., 2001;Crestanello et al., 2000). It is well known that 1,4-dihydropyridine (DHP) and its bicyclo (quinoline) and tricyclo (acridine) analogs are a well known group of calcium channel blockers that are established in the clinic as having vasodilator and anti-hypertensive functions. Potassium channel opener activities of these compounds are well known (Simşek et al., 2004;Fincan et al., 2012;Gündüz et al., 2009;Pyrko, 2008;Li et al., 2010).

D-HÁ
The molecular structure of (I) is shown in Fig. 1. The asymmetric unit consists of one half of the molecule and the complete molecule is generated from the asymmetric unit by a twofold axis which passes through the N1 and C7 atoms.

Experimental
A mixture of paraformaldehyde (1.0 mmol), 4,4-dimethyl-1,3-cyclohexanedione (2.0 mmol) and 1 mL of glacial acetic acid was refluxed in 5 mL of methanol for 8 h. Ammonium acetate (5.0 mmol) was then added and reflux was continued until the reaction was completed (monitored by TLC). The mixture was evaporated under reduced pressure, the residue was treated with 5 mL of water and 20 mL of dichloromethane. The dichloromethane extract was dried over sodium sulfate and evaporated to give the desired product. Pure crystals suitable for X-ray structure analysis were obtained by slow evaporation method using methanol as a solvent.

Refinement
H atoms bonded to C atoms were positioned geometrically and treated as riding with C-H = 0.95-0.99 Å and U iso (H) = 1.2U eq (C) for H, and C-H = 0.98 Å and U iso (H) = 1.5U eq (C) for methyl H. The crystal is a racemic twin with a BASF value of 0.3 (4).

Special details
Experimental. Absorption correction: CrysAlis RED, (Agilent, 2011) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. (Clark & Reid, 1995). 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.