Supermolecular Chiral Mesogenic Tripedes

Abstract

A novel series of chiral liquid crystalline tripedes Glucoside and Mannoside derivatives G(n) and M(n) (n=1-3) have been synthesised. The inner cores consist of methyl α-D-Glucoside G or methyl α-D-Mannoside M, regioselectively functionalised at the less hindered position C6, with tert-butyldimethylsilyl (TBDMS), hydroxyl or carboxylic acid moieties. The cores, which can acquire several flexible conformations, are attached to rod-like smectogenic-preferring cyanobiphenyl units, by means of a flexible hexanoyl spacer. These Glyco-Supermolecules exhibit chiral nematic (N*) and smectic A (SmA) phases. The combined effects of core chirality and functional groups on thermal and mesomorphic characteristics are discussed.

Orthogonal protection of saccharide polyols through solvent-free one-pot sequences based on regioselective silylations

“…The only disappointing result observed in attempted TPDPS protections was the poor yield recorded with glucal 7 (Table 2, entry 13), a surprising outcome which is somehow consistent with the very slow rate observed for the same reaction under standard conditions [39–40]. As already observed for the synthesis of 2 , the herein described conditions for regioselective TBDMS and TBDPS protections entail shorter reaction times than most of the reported protocols in the literature on monosaccharide polyols [14–18 20,41–53]; comparable silylation rates were indeed be found in a few examples, often involving relatively less polar thioaryl glycosides as the substrates and DMF as the solvent [19,54–59]. Having established the scope of TBAB-catalyzed mono silylations with a minimal excess of pyridine, some effort was devoted to ascertain the feasible exploitation of a similar strategy to either regioselective di- O -silylations or the protection of secondary alcohols in absence of primary ones (Table 3).…”

“…Taking into account several parameters such as the used amount of pyridine and TBAB, the reaction yield and its length, we elected conditions of Table 1, entry 8 as the optimized conditions. Notably, the conversion of 1 to 2 under these conditions took a much shorter time than previously reported by using the same silylating agent [14–15 18]. With optimized conditions in hand, the TBDMS regioselective installation was tested on a range of saccharide building-blocks, and good yields were achieved in short times with several polyols (Table 2, entries 1–3, 5 and 8).…”

Synthesis and Applications of Silyl 2‐Methylprop‐2‐ene‐1‐sulfinates in Preparative Silylation and GC‐Derivatization Reactions of Polyols and Carbohydrates

“…Methyl‐6‐ O ‐( tert ‐butyldimethylsilyl)‐α‐ d ‐glucopyranoside (14 a) : White powder, 97 % yield (154 mg, 0.50 mmol); 1 H NMR ([D 7 ]DMF, 400 MHz): δ= 5.17 (d, J= 4.8 Hz, 1 H; OH‐C(4)), 5.08 (d, J= 4.5 Hz, 1 H; OH‐C(3)), 4.85 (d, J= 6.5 Hz, 1 H; OH‐C(2)), 4.80 (d, J= 3.4 Hz, 1 H; H‐C(1)), 4.12 (dd, J= 11.0, 2.1 Hz, 1 H; H‐C(6a)), 3.95 (dd, J= 11.0, J= 6.2 Hz, 1 H; H‐C(6b)), 3.78 (ddd, J= 4.5, 8.5, 3.8 Hz, 1 H; H‐C(3)) 3.67 (m, J= 3.8, 2.1, 4.8 Hz, 1 H; H‐(5)), 3.52 (s, 3 H; OCH 3 ), 3.50 (t, J= 3.8 Hz, 1 H; H‐C(2)), 3.44–3.38 (ddd, J= 4.5, 8.5, 5.1 Hz, 1 H; H‐C(4)), 1.08 (s, 9 H; H‐ t BuSi), 0.26 ppm (s, 6 H; H‐MeSi); the spectroscopic data for 14 a are in agreement with those data previously reported for this compound …”

Optically Biaxial, Re‐entrant and Frustrated Mesophases in Chiral, Non‐symmetric Liquid Crystal Dimers and Binary Mixtures

“…Over the past two decades or so, tremendous progress has been made towards the development of non‐conventional liquid crystals (LCs) through the rational molecular design and bottom‐up synthesis . These hybrid mesogens differ in their shape‐anisotropy and phase transitional behavior from the conventional LCs.…”

“…It is well demonstrated that liquid‐crystal morphologies of these systems can be modulated to a large extent by varying the numbers, polarity, compatibility, size, shape, etc. of rigid cores as well as the length and parity of the spacers . For example, the influence of the latter parameter is prominently seen in LC dimers in which two mesogens are covalently bound to each other in an end‐to‐end manner via a flexible spacer .…”