Cholest-5-en-3β-yl 3-(4-ethoxyphenyl)prop-2-enoate

In the asymmetric unit of the title compound, C38H56O3, there are two symmetry-independent molecules that differ in the rotation angle along the C—O bond between the 3-(4-ethoxyphenyl)prop-2-enoate and cholest-5-en-3β-yl groups by 169.3 (3)°. In both molecules, steroid ring B adopts a half-chair conformation, rings A and C adopt a chair conformation and ring D exists in an envelope form. The two symmetry-independent molecules pack in the crystal into separate layers parallel to (-102) with their long axis parallel to the [201] direction. Short intermolecular C—H⋯O and C—H⋯π contacts are observed.

In the asymmetric unit of the title compound, C 38 H 56 O 3 , there are two symmetry-independent molecules that differ in the rotation angle along the C-O bond between the 3-(4ethoxyphenyl)prop-2-enoate and cholest-5-en-3-yl groups by 169.3 (3) . In both molecules, steroid ring B adopts a half-chair conformation, rings A and C adopt a chair conformation and ring D exists in an envelope form. The two symmetryindependent molecules pack in the crystal into separate layers parallel to (102) with their long axis parallel to the [201] direction. Short intermolecular C-HÁ Á ÁO and C-HÁ Á Á contacts are observed. 1 restraint H-atom parameters constrained Á max = 0.77 e Å À3 Á min = À0.18 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 2; y þ 1 2 ; Àz þ 2; (ii) Àx þ 1; y À 1 2 ; Àz þ 1. substances in the crystal (Tanaka et al., 1981;Dong et al., 2010). For the title compound, the authors have observed the following phase transformation sequence: Cr(1) 136.2 Cr(2) 148.9 C h 270 dec., where the numbers denote temperature of the phase transition in °C. The cholesteric phase Ch undergoes decomposition at 270°C. Of special note is the Cr(1)-Cr(2) transition at 136.2°C, which proceeds through a rapid melting of Cr(1) and an immediate solidification to Cr(2).

Related literature
This led the authors to investigate the crystal structure Cr(1) of the compound. In the crystal, there are two symmetry independent molecules A and B that vary in their ring-conformation only slightly but differ in the rotation angle along the C-O ester bond between the 3-(4-ethoxyphenyl)-2-propenoate and cholest-5-en-3β-yl groups by 169.3 (3)°. In both molecules, the π system of the phenylpropenoate unit is almost planar [for A: O1A-C28A--C31A-C36A = 3.4 (3)° and for B: O1B-C28B--C31B-C32B = -3.3 (2)°], but the average plane of the phenylpropenoate is tilted by 55.5 (3)° versus the average plane defined by the carbon atoms of ring A of the cholest-5-ene framework for molecule B and by 61.1 (3)° for molecule A. In the crystal, molecules A and molecules B define separate layers parallel to (-1 0 2). Within each layer translation related molecules form columns extended along [2 0 1] with their long molecular axis collinear with this direction. Molecules in the neighbouring columns exhibit head to tail arrangement with C-H···O interactions occurring between the 4-ethoxyphenyl group and propenoate unit (Table 1). These interactions define the strands of molecules extending in the [0 1 0] direction within the layer. The molecules in neighbouring [0 1 0] strands contact via their steroidal fragments and the dihedral angle between the mean planes of the steroidal parts of neighboring molecules is 77.3 (3)° and 83.3 (3)° for molecules A and B, respectively. The neighboring layers are packed in such a manner that contacts are formed only between molecules A and B in a head-to-head arrangement; the dihedral angle between the steroidal mean planes of these contacting molecules is 80.3 (3)°.
A conformational analysis of rings A-D was carried out, using puckering parameters developed by Cremer and Pople (1975) (Table 2). It was found that rings A and C adopt a chair conformation, ring B adopts a half-chair conformation, and ring D adopts an envelope conformation for both molecules A and B (Siri et al., 2002).

Refinement
All hydrogen atoms were placed in calculated positions with C-H distances of 0.95 -1.00 Å and refined as riding with U iso (H) = xU eq (C), where x = 1.5 for methyl and x = 1.2 for all other H-atoms. The highest peak of 0.77 e Å -3 is located at a distance of 1.30 Å and 1.22 Å from the alkyl group C25B and C27B atoms, respectively, however no reasonable model of disorder for the alkyl group could be found. In the absence of significant anomalous scattering effects Friedel pairs were merged as equivalent data. The absolute structure is based on the known absolute configuration of cholest-5-en-3βol used for the synthesis.   Intermolecular C-H···O contacts between molecules of the title compound. [Symmetry codes:

Figure 3
The layers formed by molecules A (blue), and B (green) are shown with the direction of the strand propagation (arrows).