Saturday, March 3, 2012

Synthesis of isoxazole conjugates of sugars via 1,3-dipolar cycloaddition.(Report)

Abstract: Isoxazole conjugates of sugar have been synthesized by the aid of 1,3-dipolar cycloaddition in a click chemistry approach. The sugar-derived propargyl ethers underwent 1,3-dipolar cycloadditions smoothly with in situ generated nitrile oxides from aromatic oximes in good yields. The reaction exhibited a high degree of regioselectivity.

Key words: isoxazole conjugates, 1,3-dipolar cycloadditions, nitrile oxides.

Resume : Faisant appel a une cycloaddition 1,3-dipolaire et une approche chimique qui marche tres bien, on a realise la synthese d'isoxazoles conjugues a un sucre. Les ethers propargyliques derives du sucre donnent lieu en douceur et avec de bons rendements a des reactions de cycloaddition 1,3-dipolaire avec les oxydes de nitrile generes in situ a partir d'oximes aromatiques. La reaction presente un degre eleve de regioselectivite.

Mots-cles : produits conjugues de l'isoxazole, cycloadditions 1,3-dipolaires, oxydes de nitrile.

[Traduit par la Redaction] Vaidya et al. 141

Introduction

Several compounds of natural and non-natural origin comprised of the isoxazole moiety possess a broad spectrum of biological properties viz., fungicidal, antibacterial, antiinflammatory, anti-allergic, anti-tumor, herbicidal, etc. The isoxazole class of compounds are also synthetically important as 1,3-dicarbonyl equivalents (1). Among the plethora of protocols reported for the synthesis of the isoxazole skeleton, two major routes are the 1,3-dipolar cycloadditon of alkenes and alkynes with nitrile oxides and the reaction of hydroxylamine with a three-carbon atom component, such as 1,3-diketone or an [alpha],[beta]-unsaturated ketone. 1,3-Dipolar cycloaddition has proven particularly valuable for the construction of complex five-membered conformationally rigid heterocycles (2). Isoxazoles, also among the five-membered heterocycles, can be accessed by 1,3-dipolar cycloaddition reaction. In particular, nitrile oxides undergo cycloaddition with alkynes resulting in good yields of isoxazoles (3). A similar class of compounds, i.e., triazoles, have been synthesized via 1,3-dipolar cycloaddition of azides and alkynes. This reaction has been considered as the prototype of click chemistry (4). There are several excellent contributions from various …

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