Ethyl 2,6-bis(4-chlorophenyl)-1-isocyano-4-oxocyclohexanecarboxylate

In the title compound, C22H19Cl2NO3, the central six-membered ring is in a twist-boat conformation. The two aryl groups are in equatorial positions, trans to each other and with a dihedral angle of 77.50 (2)° between them. One of the least hindered –CH2– groups and one of the aryl-substituted C atoms, with its axial H atom, are in the flagpole positions. The ethoxycarbonyl group is in an equatorial position and is cis to the second aryl group. In the crystal, molecules are linked via weak C—H⋯O hydrogen bonds, forming chains along [010].

In the title compound, C 22 H 19 Cl 2 NO 3 , the central sixmembered ring is in a twist-boat conformation. The two aryl groups are in equatorial positions, trans to each other and with a dihedral angle of 77.50 (2) between them. One of the least hindered -CH 2 -groups and one of the aryl-substituted C atoms, with its axial H atom, are in the flagpole positions. The ethoxycarbonyl group is in an equatorial position and is cis to the second aryl group. In the crystal, molecules are linked via weak C-HÁ Á ÁO hydrogen bonds, forming chains along [010].
Financial support of this research by the Science and Technology Development Program Foundation of Jilin Province (No. 20140204022NY) and the Interdisciplinary Innovation Fund of Jilin University (No. 450060481143) is gratefully acknowledged.
Supporting information for this paper is available from the IUCr electronic archives (Reference: LR2127).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.Hydrogen atoms were generated in idealized positions (according to the sp2 or sp3 geometries of their parent carbon), and then refined using a riding model with fixed C-H distances (C-H = 0.95-1.00 Å) and with Uiso(H) = 1.2Ueq(C).

Results and discussion
[5+1] annulation is a novel strategy for the construction of six-membered cyclic compounds and total synthesis of natural products (Rowland & Gill, 1988;Wu et al., 2011;Li et al., 2011). The regiospecific [5+1] annulation reactions have drawn much attentions and both the five-carbon 1,5-bielectrophiles and the one-atom nucleophiles been explored extensively (Bi et al., 2005;Zhao et al., 2006;Fu et al., 2009;Xu et al., 2012). We have been dealing with functionalized ketene dithioacetals for several years and have succeeded in the preparation of six-membered aromatic and heterocyclic compounds based on [5C+1X] annulations (Zhang et al., 2010;Tan et al., 2009). The aromatic cyclic compounds are analogues of phenylalanine (Phe) which are potential moieties for the synthesis of peptide analogues with controlled fold in the backbone. The constrained ring systems play important roles in restricting torsional angle χ1 and in peptide receptor recognition processes (Aleman et al., 2009).
The crystal structure of title compound, a phenyl substituted highly constrained cyclohexane analogue of Ph, is reported in this paper. Due to the steric hindrance, the oxocyclohexane is in a twist-boat conformation (Fig. 1) lead the formation of a comparable stable boat conformation of this compound.

Figure 1
View of the molecular structure of the title compound with labeling and displacement ellipsoids drawn at the 30% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq