3-Arylisoxazolyl-5-carboxylic acid and 5-(Hydroxymethyl)-3-aryl-2-isoxazoline as molecular platforms for liquid-crystalline materials

Aline Tavares,Paolo R Livotto,Paulo F B Gonçalves,Aloir A Merlo

doi:10.1590/s0103-50532009000900025

Abstract

The synthesis of the molecular platform for liquid-crystalline materials based on 3-arylisoxazolyl-5-carboxylic acid (1) and 5-(hydroxymethyl)-3-aryl-2-isoxazoline (2) is described. The key intermediates 1 and 2 are obtained by [3+2] 1,3-dipolar cycloaddition reaction between an arylnitrile oxide and an acrylic acid and allylic alcohol as the dipolarophile. The liquid crystals (LC) compounds are synthesized through a "molecular elongation strategy" from the initial isoxazolinic core by connecting the arylacetylene moiety obtained from the Sonogashira reaction. Under these conditions, the series of liquid crystals 5a-c, 6, 7a-g and 8a-d have been successfully synthesized in fair to good yields. The final compounds display nematic and smectic liquid-crystalline properties. The structural properties of the series of the liquid crystals has been studied using DFT methods at level B3LYP/6-31G(d,p). The equilibrium geometries in the gas phase are presented and analyzed.

Highlights

The [3+2] 1,3-dipolar cycloaddition reaction of a nitrile oxide to an alkene or alkyne has proven to be extremely useful in the preparation of a variety of compounds in organic chemistry
Our previous results showed that the introduction of an isoxazoline ring flanked by aromatic rings or polar groups opened a route to prepare useful intermediates in the field of liquid crystals.[6]
Based upon the considerations discussed above, we report a convenient and practical route to the synthesis of isoxazoline ring platform for liquid crystal (LC) materials

Summary

Introduction

The [3+2] 1,3-dipolar cycloaddition reaction of a nitrile oxide to an alkene or alkyne has proven to be extremely useful in the preparation of a variety of compounds in organic chemistry. The LC 5-(hydroxymethyl)3-aryl-2-isoxazolyl benzoates 7c-g and 8a-d displayed monotropic liquid-crystalline phase where the smectic C and nematic mesophases were observed in these series (Table 1), respectively.

Results

Conclusion