Cyclohexenyl triflates and arylboronic acids in palladium-catalysed cross-couplings. Synthesis and transition temperatures of some fluoro-substituted biphenylylcyclohexenes

Abstract

A range of liquid crystalline materials with low melting points have been prepared that incorporate a cyclohexene ring in the core. Substituted cyclohexanones were converted into their vinyl triflate derivatives by generation of the lithium enolates using LDA and subsequent quenching with N-phenyltriflamide. The vinyl triflates were then coupled to a range of fluoro-substituted arylboronic acids (generated using ortho-directed metallation techniques at low temperature) in a novel reaction to provide liquid crystals with very low melting points. The lateral fluoro-substituents play an important role in modifying the mesomorphic and physical properties of the materials; the effects of the position of fluoro substitution on the mesomorphic behaviour is discussed.