Partial cone conformer of 25,27-bis[(methoxycarbonyl)methoxy]-26,28-dipropoxycalix[4]arene

Molecules of the title compound, C40H44O8, adopt a partial cone conformation. The dihedral angles between the planes of the aromatic rings and the mean plane through the methylene C atoms bridging the aromatic rings are 35.74 (7), 85.86 (5), 87.77 (4) and 89.95 (5)°. Two opposite aryl rings are approximately parallel to each other; the others are at an interplanar angle of 52.41 (6)°. Intra- and intermolecular C—H⋯O hydrogen bonds stabilize the molecular conformation and the crystal packing. Two C atoms of one propoxy chain are disordered over two positions; the site occupancy factors are ca 0.66 and 0.34.

Molecules of the title compound, C 40 H 44 O 8 , adopt a partial cone conformation. The dihedral angles between the planes of the aromatic rings and the mean plane through the methylene C atoms bridging the aromatic rings are 35.74 (7), 85.86 (5), 87.77 (4) and 89.95 (5) . Two opposite aryl rings are approximately parallel to each other; the others are at an interplanar angle of 52.41 (6) . Intra-and intermolecular C-HÁ Á ÁO hydrogen bonds stabilize the molecular conformation and the crystal packing. Two C atoms of one propoxy chain are disordered over two positions; the site occupancy factors are ca 0.66 and 0.34. Mo K radiation = 0.09 mm À1 T = 298 (2) K 0.37 Â 0.18 Â 0.08 mm
to the ethyl ester derivatives of the calix[4]arene (Iwamoto & Shinkai, 1992;Arena et al., 1997) since they are one of the most versatile intermediates for building highly preorganized receptors. It has been shown that the conformational distribution in the exhaustive O-alkylation of the calix[4]arene depends upon the reaction conditions, the para substituent of the calix[4]arene, and the steric requirement of the agent (Pappalardo et al., 1992;Ferguson et al., 1993). In the O-alkylation, the cone and 1,3-alternate conformers are often obtained via the metal template effect using potassium and caesium ions, respectively (Yamato et al., 1998). However, both partial cone and cone conformers were isolated instead of the 1,3-alternate conformer when treatment 25,27-dihydroxy-26,28-dipropoxycalix[4]arene with methyl bromoacetate using caesium carbonate as a base in acetone.
In the crystal structure there are intra-and intermolecular C-H···O hydrogen bonds (Table 1), which stabilize the partial cone conformation and the crystal packing.

Experimental
A mixture of 25,27-dihydroxy-26,28-dipropoxycalix[4]arene (0.200 g, 0.39 mmol), anhydrous caesium carbonate (0.190 g, 0.59 mmol) and methyl bromoacetate (0.11 ml, 1.17 mmol) in dry acetone (10 ml) was refluxed under nitrogen for 8 h and cooled to room temperature. After removal of the solvent under reduced pressure, the residue was treated with 5% aqueous hydrochloric acid and extracted with dichloromethane. The organic layer was washed with saturated sodium hydrogen carbonate and brine, dried over anhydrous magnesium sulfate. The solvent was removed under reduced pressure and the residue was purified by flash column (silica gel, EtOAc/petroleum ether = 1:5) to give conformer (I) (R f = 0.7) and comformer (II) (R f = 0.4) in 48% and 39% yields, respectively. Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of methanol into a dichloromethane solution at 273 K.
supplementary materials sup-2 Atoms C19 and C20 are disordered over two positions (C19/C19' and C20/C20'), with refined occupancies of 0.337 (5) and 0.663 (5). One of the two CH 2 -CH 3 distances of the disordered C-atoms (C18-C19) was restrained to 1.54 (1) Å. Fig. 1. The molecular structure of the title compound, showing the atomic numbering scheme and displacement ellipsoids drawn at the 30% probability level for non-H atoms. The major occupied site of the disordered side chain is drawn with dashed bonds.

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 > 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.