Design and Synthesis of C3-Symmetric Chiral Dopants for Nematic Liquid Crystals Based on the I2-Promoted Cyclodearomatization of Alkyne-Linked Benzofurans

Abstract

For the efficient geometry control of chiral nematic liquid crystals (N*LCs), a variety of chiral furopyran derivatives 1 with three aromatic groups fixed in a pseudo-C₃-symmetric fashion was designed as novel chiral dopants (CDs) and successfully synthesized from the alkyne-linked benzofuran systems 2 in excellent yields by the newly developed I₂-promoted iodination–dearomatizative [4 + 2] cycloaddition cascade reaction. The subsequent structural diversification of the thus obtained 1 was achieved by various coupling methods applied for the iodoalkene moiety. The high performance of 1 as CDs was demonstrated in JC-1041XX/5CBs (1:1 wt ratio) as achiral host LCs, leading to the discovery of 1el with a naphthofuran and long-chain alkyl unit that exhibited an extremely large molecular helical twisting power (molecular HTP or β_M) of −203 μm^–1 and produced cholesteric blue phases (BP I and BP II), namely, N*LC phases, comprising a higher-order supramolecular network.