Crystal structures of (E)-(3-ethyl-1-methyl-2,6-diphenylpiperidin-4-ylidene)amino phenyl carbonate and (E)-(3-isopropyl-1-methyl-2,6-diphenylpiperidin-4-ylidene)amino phenyl carbonate

The title compounds are the 3-ethyl, (I), and 3-isopropyl, (II), derivatives of (1-methyl-2,6-diphenylpiperidin-4-ylidene)amino phenyl carbonate. The main difference in the conformation of the two compounds is the angle of inclination of the phenoxycarbonyl ring with respect to the piperidine ring mean plane, with a dihedral angle of 2.05 (8)° in (I) and 45.24 (13)° in (II).


Structural commentary
The molecular structure of compound (I) is shown in Fig. 1. The piperidine ring adopts a chair conformation. The attached ISSN 1600-5368 phenyl rings (C7-C12 and C13-C18) are twisted away from the mean plane of the piperidine ring by 85.82 (8) and 85.84 (7) . The two phenyl rings are oriented to each other with a dihedral angle of 52.87 (8) . The phenoxy ring (C22-C27) is almost coplanar with the piperidine ring mean plane with a dihedral angle of 2.05 (8) . The sum of the bond angles around atom N1 (331.9 ) is in accordance with sp 3 hybridization. The ethyl group substituted at position 5 of the piperidine moiety is in an equatorial orientation.
The molecular structure of compound (II) is shown in Fig. 2. The piperidine ring also adopts a chair conformation. The attached phenyl rings (C7-C12 and C13-C18) are twisted away from the mean plane of the piperidine ring by 87.98 (12) and 86.42 (13) . The two phenyl rings are oriented to each other with a dihedral angle of 60.51 (14) . In (II) the phenoxy ring (C23-C28) is no longer coplanar with the mean plane of the piperidine ring but inclined to it by 45.24 (13) . The sum of the bond angles around atom N1 (335.6 ) is in accordance with sp 3 hybridization. The isopropyl group substituted at position 5 of the piperidine moiety is in an equatorial orientation.
For both compounds (I) and (II), the bond lengths and bond angles are comparable with the values reported for the 3methyl derivative (III), (E)-3-methyl-1-methyl-2,6-diphenylpiperidin-4-one O-phenoxycarbonyl oxime (Raghuvarman et al., 2014). The overall conformation of compound (III) is very similar to that of compound (II), with the phenoxy ring inclined to the mean plane of the piperidine ring by 32.79 (9) , compared to 45.24 (13) in (II).

Supramolecular features
In the crystal of (I), pairs of C-HÁ Á ÁO hydrogen bonds link the molecules, forming inversion dimers with R 2 2 (14) loops. The dimers are linked via C-HÁ Á Á interactions, forming a three-dimensional network ( Fig. 3 and Table 1).
In the crystal of (II), there are no significant intermolecular interactions present. This is similar to the situation in the crystal of compound (III). The packing in (II) is illustrated in Fig. 4 The molecular structure of compound (II), with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
A view along the a axis of the crystal packing of compound (I). The C-HÁ Á ÁO hydrogen bonds are shown as dashed lines (see Table 1 for details).

Figure 1
The molecular structure of compound (I), with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 4
A view along the a axis of the crystal packing of compound (II).
reaction mixtures were diluted with water (20 ml) and extracted with dichloromethane (2 Â 20 ml). The combined organic layers were washed with water (2 Â 20 ml), brine solution (20 ml), dried over anhydrous sodium sulfate (5 g), filtered and concentrated under reduced pressure. The crude products were purified by column chromatography over silica gel (100-200 mesh) eluted with a solvent system of ethyl acetate-petroleum ether (2:98). The pure fractions were collected and concentrated under reduced pressure to give white solids of (I) (yield 0.60 g, 86%) and (II) (yield 0.56 g, 82%), which were recrystallized from a DMF-water mixture (9:1) to give colourless block-like crystals of (I) and (II), respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were positioned geometrically and allowed to ride on their parent atoms: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C-methyl) and = 1.2U eq (C) for other H atoms. For both compounds, data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008 PLATON (Spek, 2009). Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained

(II) (E)-(3-Isopropyl-1-methyl-2,6-diphenylpiperidin-4-ylidene)amino phenyl carbonate
Crystal data 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.