Synthesis of Potential Liquid Crystals With Cholesterol Fragment by Wittig Reaction

Abstract

Liquid crystals are substances that owing to the features of their structure and physical properties are of interest not only as objects for theoretical research, but also significantly important practically due to the possibilities of their effective application in various brunches of industry, medicine, in household etc. Among the known classes of liquid crystals, substances known as cholesterics are an important group.
 Cholesteric liquid crystals demonstrate very high optical activity, that significantly exceeds the optical activity of most other known classes of organic compounds. Their ability for appreciable change of color at change of the temperature and environment composition is also practically important.
 Among all compounds belonging to the class of cholesterics an important place possess cholesterol derivatives, especially cholesterol esters. Therefore, the elaboration of new methods of their synthesis and the introduction of new functional groups into their molecules are an urgent tasks indeed.
 This work is devoted to the investigation of the possibility of synthesis of new cholesterol derivatives, namely cholesteryl esters of unsaturated acids by the Wittig reaction - the interaction of various classes of aldehydes with phosphonium salts, with the intermediate formation of phosphorus ylides - alkylidene phosphoranes. We found that the Wittig reaction is a convenient method for the synthesis of cholesteryl esters of unsaturated carboxylic acids. We have developed methods for the synthesis of potential cholesteric liquid crystals by the Wittig reaction, which use a phosphonium salt containing a cholesterol fragment and corresponding aldehydes. The process proceed without the release of an intermediate compound – alkylidene phosphorane, which reduces the labor intensity of the method.
 The application of various aldehydes enables the easily obtaining of cholesteryl esters of unsaturated acids containing various aliphatic, aromatic and heterocyclic fragments in the acid radical. The reaction takes place in mild conditions, without using of high temperatures or aggressive environments. The resulting esters show signs of mesophase formation, which is a confirmation of their liquid crystalline properties.