Materiais moleculares funcionais contendo n-heterociclos - capes

LSYC146630 LSYC_036_007 Techset Composition Ltd, Salisbury, U.K. 1/20/2006952G. Conte et al.phases, because most of the usual heteroatoms (S, O, and N) introduced are[5 – 7]chemically classified as more polarizable than carbon.In particular, [1,2,3]-triazoles are useful targets in chemical synthesisbecause they have been associated with a wide variety of interesting properties.These un-natural N-heterocyclic compounds with large biologicalactivity exhibit great potential in material chemistry as dyes, corrosion inhibitors,photostabilizers, and photographic materials. [8,9] In this context, we haveexplored the synthesis of liquid-crystalline materials based on 1,4-dissubstituted[1,2,3]-triazole, aiming at new highly anisometric organic architectureswith special properties (Figure 1).The most general methodology described in literature for the synthesis offive-membered ring heterocycles is the 1,3-dipolar cycloaddition reaction. Inparticular, when the reaction occurs between alkyl or aryl azides and terminalacetylenes, [1,2,3]-triazole are obtained. [10,11] Combinations of substituentson the azide and the alkyne allow the preparation of many N-substituted structures.If the cycloaddition is thermally conduced, a mixture 1:1 of the 1,4- and1,5-regioisomers is usually obtained. To improve the 1,4-regioselectivity,reactions were carried out using a catalytic amount of Cu(I) or Cu(II) saltsand sodium ascorbate, with water as solvent or still in encapsulatedsystems [12,13] (Scheme 1). The catalytic mechanism has been investigated indetail by Fahmi et al., who recently proposed a consistent cycle. [14]Figure 1.1,4-Diaryl [1,2,3]-triazole liquid crystals.