Dimethyl 2,6,8-trimethyl-1,2-dihydroquinoline-2,4-dicarboxylate

The title compound, C16H19NO4, the hydrogenated ring adopts a twisted conformation. In the crystal, intermolecular C—H⋯O hydrogen bonds link the molecules into centrosymmetric R 2 2(10) dimers. These dimers are further connected via intermolecular N—H⋯O hydrogen bonds, forming infinite double chains along [001].

The title compound, C 16 H 19 NO 4 , the hydrogenated ring adopts a twisted conformation. In the crystal, intermolecular C-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric R 2 2 (10) dimers. These dimers are further connected via intermolecular N-HÁ Á ÁO hydrogen bonds, forming infinite double chains along [001].
In the title molecule, illustrated in Fig In the crystal of the title compound intermolecular C-H···O hydrogen bonds (Table 1) link the molecules into R 2 2 (10) dimers centered about an inversion center (Bernstein et al., 1995). These dimers are further connected via intermolecular N-H···O hydrogen bonds (Table 1)
The mixture was stirred at room temperature for 6 d until the starting material was completely consumed as monitored by TLC. The resultant residue was directly purified by flash chromatography on silica (EtOAc:Cylohexane 2:98) and gave, in 60% yield, a pale yellow solid. This solid was recrystallized over pentane and ethyl acetate (70:30) to give a pale yellow crystalline solid; R f 0.25 (2:1 Cyclohexanone/EtOAc); mp. 420-421 K (Rueping & Gültekin, 2009).

Refinement
The C14 and C16 methyl H-atoms were positioned geometrically and constrained to ride on their parent atoms: C-H = 0.96 Å with U iso (H) = 1.5U eq (C). The remaining H-atoms were located in a difference Fourier map and were refined isotropically. Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.  Table 1 for details).

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 > 2sigma(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.