5,11,17,23-Tetrakis(1,1-dimethylethyl)-26,28-dihydroxycalix[4]arene-25,27-monothiacrown-3

The title calix[4]arene compound [systematic name: 3,9,15,34-tetra-tert-butyl-19,29-dioxa-24-thiahexacyclo[15.13.7.17,11.132,36.05,30.013,18]nonatriaconta-1(30),2,4,7,9,11(39),13,15,17,32,34,36(38)-dodecaene-38,39-diol], C52H70O4S, displays a cone-like conformation, the opposite arene rings bridged by the monothiacrown-3 unit are nearly parallel [dihedral angle = 16.01 (18)°], whereas the other opposite arene rings are twisted to each other at an angle of 74.41 (17)°. Intramolecular O—H⋯O hydrogen bonds help to stabilize the molecular structure. In the crystal, a C—H⋯π interaction occurs. One of the tert-butyl groups is disordered over two sets of sites with a site-occupancy ratio of 0.70:0.30.

Cg is the centroid of the C30-C35 benzene ring. In particular, Calix-Crown ethers in which the proper-sized crown rings are incorporated into the calixarene framework have attracted intense interest as a selective extractant for specific metal ions (Casnati et al., 1995;Csokai et al., 2006)).

D-HÁ
In this work, the title p-tert-butylcalixarene-thiacrown in the cone conformation was synthesized, and this is the first report of the crystal structure for the calixarene-thiacrown.
The title compound (I) is shown in Fig 1. The calixarene retains a distorted cone conformation in the solid state. The opposite arene rings A and C that bear the substituents are almost parallel to each other, whereas the other rings B and D include dihedral angles of 74.41 (17)°. Moreover, the plane defined by four methylenic bridges was chosen as a reference plane. The two rings bear the substituents are more vertical than the other two rings. The carbon atoms C1 and C5 in the alkyl chain points towards the exterior of the macrocycle and the torsion angles around the O1-C1, O2-C5 and bonds do not deviate from ideal syn values by about 5°. An additional close intramolecular hydrogen bonds between O4 and O2, O3 and O1 stabilize this conformation.

Experimental
A mixture of p-tert-butylcalix[4]arene dibromides (Li et al., 1999) (137 mg, 0.15 mmol) and Na 2 S.9H 2 O (48 mg, 0.20 mmol) in DMF (5 ml) was stirred at 333 K for 5 h. After cooling the reaction mixture to room temperature, it was quenched by water and extracted with dichloromethane. The organic layer was then washed with brine, dried over Na 2 SO 4 , and filtered. The solvent was evaporated in vacuo, and the residue was purified by column chromatography on silica gel from petroleum ether/dichloromethane. Petroleum ether/dichloromethane ( Single crystals of (I) suitable for X-ray diffraction analysis were obtained by slow diffusion of petroleum ether into a chloroform solution at 298 K.

Refinement
Hydroxy H atoms were located in a difference Fourier map and refined isotropically. Other H atoms were positioned geometrically with C-H = 0.93-0.97 Å and allowed to ride on their parent atoms, U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for the others.

Figure 1
The structure of the title compound.

Special details
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.