Silicon in organic synthesis. 14. Five ring annulation processes based upon thermal rearrangement of (1-trimethylsilylcyclopropyl)ethylenes

Pyrolysis of (1-trimethylsilylcyclopropyl)ethylenes affords silyl substituted cyclopentenes in high yield. Subsequent reaction of these products with varied electrophiles forms the basis of a new and versatile five-ring annulation sequence.     

Twist-bend nematics,liquid crystal dimers,structure–property relations

ABSTRACT

One of the current challenges in liquid crystal science is to understand the molecular factors leading to the formation of the intriguing twist-bend nematic phase (N_TB) and determine its properties. During our earlier hunt for the N_TB phase created on cooling directly from the isotropic phase and not the nematic phase, we had prepared 30 symmetric liquid crystal dimers. These had odd spacers and methylene links to the two mesogenic groups; desirable but clearly not essential features for the formation of the N_TB. Here, we report the phases that the dimers exhibit and their transition temperatures as functions of both the lengths of the spacer and the terminal chains. In addition we describe the transitional entropies, their optical textures, the X-ray scattering patterns and the ²H NMR spectra employed in characterising the phases. All of which may lead to important properties of the twist-bend nematic phase.