Enantioselective Synthesis of 3‑Aryl-3-hydroxypropanoic Esters as Subunits for Chiral Liquid Crystals

Chiral
liquid crystals (LCs) with their unique optical and mechanical
properties are perspective functional soft materials for fundamental
science and advanced technological applications. Herein, we introduce
the chiral 3-aryl-3-hydroxypropanoic ester moiety as a versatile building
block for the preparation of LC compounds. Three chiral subunits differing
in the aromatic part were obtained through asymmetric transfer hydrogenation
using Ru(II) complexes with ee from 98% to >99%. Chiral LC compounds
of diverse topologies were further prepared without deterioration
of the ee during the synthesis. The mesomorphic behavior of rod-shaped,
bent-shaped flexible dimeric, and polycatenar LCs is consistent with
their topologychiral nematic and smectic phases were identified
as well as the rarely observed twist grain boundary A and blue phases.
The utilization of synthetic chiral building blocks offers the possibility
of fine tuning the intermolecular interactions by subtle changes in
the molecular structure as well as the preparation of the corresponding
racemic forms. This paves the way for the study of self-organization
and the structure–property relationship in chiral soft materials.