Materiais moleculares funcionais contendo n-heterociclos - capes

LSYC146630 LSYC_036_007 Techset Composition Ltd, Salisbury, U.K. 1/20/2006954G. Conte et al.Table 1.Synthetic yields and respective phases for compounds 3a–eProduct Yield (%) Phases transitions (8C) a3a 56 Cr 137.6 SmC 221.6 N 226.0 I3b 65 Cr 159.1 SmC 216.2 I3c 74 Cr 183.3 SmC 245.5 I3d 80 Cr 148.0 SmC 194.2 I3e 98 Cr 144.5 SmC 164.1 SmA 168.6 Ia Observed by polarized optical microscopy.liquid-crystalline molecules 3a–e, several procedures using the click reaction(Cu(I)-catalyzed) were tested to selectively prepare the 1,4-disubstitutedregioisomer. Best results were achieved by using a mixture of ethanol/water and catalytic amounts of Cu(I) and triethylamine (TEA) asadditive. [12] This way the goals were obtained in high degree of purity andin good chemical yields (Table 1).The structure assignment of [1,2,3]-triazole was done based on its 1 H and13 C NMR spectra and comparing them with the relevant literature data. [16,17]The 1 H NMR spectra for compounds 3a–e showed a single signal for thetriazole-H-5, which varied from 7.99 up to 8.32 ppm. In addition, 13 CNMRspectra showed the chemical shifts for C-5 and C-4 of the triazole ring inthe range from 148.68 up to 148.00 ppm and from 132.5 to 130.65 ppm,respectively. Such values are very similar to those found in the literaturefor the 1,4-regioisomer. [18] The other signals of 1 H and 13 C NMR are incomplete agreement with the assigned structures, and they are listed in theexperimental section.The transition temperatures, phase attribution, and texture observationwere investigated by polarized optical microscopy. As expected, all thecompounds showed liquid-crystalline behavior (Table 1), in particular thelayered smectic C phase.In conclusion, this article demonstrated a general, straightforward, andefficient protocol for the regioselective synthesis of functionalized 1,4-disubstituted [1,2,3]-triazoles. The method consists in a Cu(I)-catalyzed 1,3-dipolar cycloaddition of aryl azides to terminal arylacetylenes (clickreaction). This versatile synthetic route allowed us to obtain non linear 1,4-disubstituted liquid-crystalline compounds based on [1,2,3]-triazole in goodchemical yields and purity.EXPERIMENTALThe melting points, thermal transitions, and mesomorphic textures were determinedusing an Olympus BX50 microscope equipped with a Mettler ToledoFP-90 heating stage and a PM-30 exposure control unit. Each analytical