Abstract
In this article, we synthesized a novel dendritic 2-oxazoline, 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)-4,5-dihydro-1,3-oxazole), and its amide precursor N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide. Of the distinct synthetic routes explored, it was established that the direct amidation of esters with sodium methoxide followed by the dehydrative cyclisation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as oxidizing agent and triphenylphosphine was the most efficient route to synthesize the dendritic 2-oxazoline. Besides, N-(2-hydroxyethyl)-3,4,5-tris(4-dodecyloxybenzyloxy)benzamide exhibited a monotropic columnar mesophase, whilst the dendritic 2-oxazoline does not exhibited a liquid crystalline mesophase. At the end, the first attempts to polymerize the 2-oxazoline monomer via cationic ring opening polymerization showed promising results. Therefore, the dendritic 2-oxazoline could be used as a mesogenic monomer in the synthesis of side-chain liquid-crystalline polyoxazolines that might self-assembly into columnar structures.
Highlights
In this article, we synthesized a novel dendritic 2-oxazoline, 2-(3,4,5-tris(4-dodecyloxybenzyloxy) phenyl)-4,5-dihydro-1,3-oxazole), and its amide precursor N-(2-hydroxyethyl)-3,4,5-tris(4dodecyloxybenzyloxy)benzamide
4,5-Dihydro-1,3-oxazoles, more commonly known as 2-oxazolines or Δ2-1,3-oxazolines, are five-membered cyclic imino ethers which were synthesised for the first time in 1 8841, their structure was not clearly elucidated until 5 years later by G abriel[2]
Different synthetic routes have been explored in this work to synthesize 2-(3,4,5-tris(4-dodecyloxybenzyloxy)phenyl)2-oxazoline (TAPOx), considering the number of involved stages
Summary
We synthesized a novel dendritic 2-oxazoline, 2-(3,4,5-tris(4-dodecyloxybenzyloxy) phenyl)-4,5-dihydro-1,3-oxazole), and its amide precursor N-(2-hydroxyethyl)-3,4,5-tris(4dodecyloxybenzyloxy)benzamide. Different applications have been reported for 2-oxazolines: they have been utilised as ligands in asymmetric catalysis[5,6], as synthetic intermediates[7], as structural components of natural products or as protecting groups for carboxylic acid functionalities[8] These cyclic organic compounds are principally employed to build-up substituted poly(2-oxazoline)s (PAOx) with a well-defined structure by living cationic ring-opening polymerization (CROP)[3,9,10,11]. The similar chemical structure of the resulting poly(2-oxazoline)s to natural polypeptides confers to these polymers an excellent biocompatibility, which together with their low viscosity and high stability make this kind of polymeric materials an ideal candidate in biomedical applications As proof of these exceptional properties, Moreadith and co-workers reported recently a drug loaded PAOx that has been tested as a therapeutic agent in the Phase 1 clinical trials of Parkinson’s d isease[12]. This group conducted a wide investigation on the self-assembly of several minidendritic
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