Tunable Chiral Reaction Media Based on Two-Component Liquid Crystals: Regio-, Diastereo-, and Enantiocontrolled Photodimerization of Anthracenecarboxylic Acids

Abstract

Three kinds of enantiopure amphiphilic amino alcohols (1a-c) were newly synthesized, of which the stereochemistry of the stereogenic carbons adjacent to the amino (C2) and hydroxy (C1) groups was systematically varied. By using these amino alcohols and four photoreactive carboxylic acids, 12 kinds of salts were prepared. The structure and thermal behavior of the salts were thoroughly investigated by various techniques, which revealed that the stereochemistry of the amino alcohol unit has significant effects on the properties of the salts; the salts of 1a with (1R,2S)-configuration did not exhibit any liquid crystal (LC) phase but showed high crystallinity, whereas 1b and 1c with (1S,2S)- and (1S)-configurations, respectively, generally afforded stable LC salts with smectic structure(s). Within the matrix of these amphiphilic salts, the in situ photodimerizations of 2-anthracenecarboxylic acid (2c) and 1-anthracenecarboxylic acid (2d) were conducted by the irradiation with UV/vis light (500 W, a high-pressure mercury arc lamp, >380 nm). Concerning reactivity and regio-/diastereo-/enantioselectivities, the LC phases were found to be superior to isotropic and crystalline phases. For the two substrates 2c and 2d, every LC phase promoted the photodimerization with unprecedentedly high head-to-head selectivity. Particularly in the case of 2c, diastereoselecitivity (syn(HH) vs anti(HH)) could be rationally controlled by the choice of the amino alcohol unit and mesophase (syn(HH):anti(HH) = 61:37 to 26:72). Moreover, one of the LC phases exhibited by 1b·2c afforded the anti(HH)-dimer of 2c with excellent enantioselectivity (up to 86% ee). On the basis of the hypothesis that the present photochemical outcome arises from the preorientation of the substrates, a preliminary structural model of these LCs was proposed.

Macroscopic ordering of helical pores for arraying guest molecules noncentrosymmetrically

“…As we previously reported, conformational preferences of T and T′ are quite different from each other, where T tends to adopt a more flatten conformation (=larger dihedral angle θ in Supplementary Fig. 11a ) due to the steric hindrance between the phenyl and methyl groups 45 . Such a flatten conformation would facilitate the stacking of the salt pairs of F and T , as suggested by the diffraction due to π -stacking ( Fig.…”

Knotting a molecular strand can invert macroscopic effects of chirality

“…It may be that this high knotting efficiency is a consequence of the liquid crystal environment aiding folding by restricting the conformations accessible to the strand outside of the knotting pathway. Other phenomena attributed to crowding effects in liquid crystals include rate and stereochemical enhancement in chemical reactions 58 and the synthesis of helical polymers 59 .…”

Organische Chemie 2011

“…Über supramolekulare, ionische Wechselwirkungen werden auch Anthracencarbonsäuren an Aminoalkohole gebunden. Eine kolumnare Phase wird für das (S,S)‐Derivat (19) beobachtet, nicht jedoch für das (R,S)‐Diastereomer 25. Die Mesophase eignet sich für die photochemische, diastereoselektive Dimerisierung der Anthracencarbonsäure, die bevorzugt syn ‐Produkte liefert (Abbildung 7).…”