SYNTHESIS AND PROPERTIES OF CHOLESTERYL ESTERS BEARING 32-MEMBERED AND 16-MEMBERED CROWN-ETHERS

The cholesteryl esters (3b and 3a) of 5-carboxy-1,3-phenylene-16-crown -5 and 5-carboxy-4,6-dichloro-1,3-phenylene-16-crown-5 show cholesteri c liquid crystalline behavior but only upon heating samples that were rapidly cooled from the isotropic melt in the case of 3a and a monotro pic phase for 3b. The dichloro compound 3a was formed by treatment of the corresponding acid 2 with SOCl2 first and then cholesterol; it is believed that the SOCl2 was contaminated with SO2Cl2, leading to the c hlorination of the aromatic ring. The dichloro compound 3a was structu rally characterized using single crystal X-ray diffraction. 3a crystal lizes in the orthorhombic space group P2(1)2(1)2(1) With unit cell par ameters of a = 12.76(4) Angstrom, b = 17.511(5) Angstrom, and c = 18.2 13 Angstrom. Use of freshly opened SOCl2 produced 3b. The reaction of the acid 2 and cholesterol in the presence of dicyclohexylcarbodiimide yielded the acylisourea 4 as the major product (64%) along with 3b (3 6%) upon treatment with cholesterol. The dicholesteryl ester 9 of bis( 5-carboxy-1,3-phenylene)-32-crown-10 (8a) was also synthesized, and by differential scanning calorimetry (DSC) and polarized optical microsc opy no liquid crystalline behavior was observed with this system. Appa rently the presence of the semirigid crown in the molecule prevents th e two cholesteryl moieties from organizing in independent helices. The complexation ability of this cholesteryl crown (9) with methyl violog en bis(hexafluorophosphate) ([paraquat]. 2[PF6]) (12) in acetone has b een examined by H-1 NMR spectroscopy; it showed weaker binding than it s simple dimethyl ester analog 8b.