The synthesis and transition temperatures of some difluoro-substituted cyclohexanes

Abstract

A range of trans-1,4-disubstituted cyclohexane materials has been prepared that incorporates a difluoromethylene unit as part of the cyclohexane ring. These compounds illustrate the great difference in mesogenic behaviour between compounds with fluoro-substituents in an alicyclic environment and those with fluoro-substituents in aromatic rings. An improved fluorination method, which involves the use of hydrogen fluoride–pyridine, has been developed and provides high yields of fluorinated materials. Highly efficient palladium-catalysed cross-coupling reactions involving arylboronic acids have been used to provide the final liquid crystal materials. The important issue of the cis and trans isomers of these compounds is discussed and the structures of the fluorinated materials are discussed with reference to their interesting ¹H and ¹³C NMR spectra.