Triazole Units

As the Diels-Alder reactions of 2( lff)-pyrazinones with richly substituted acetylenes can be used to generate diversely substituted pyridines and pyridi-nones, these cyclo additions were investigated under microwave irradiation conditions on the 1,2,3-triazole decorated pyrazinone scaffold. As a proof of concept, the pyrazinones bearing a 1,4-disubstituted-1,2,3-triazole unit, linked via a C-0 bond, were reacted with the symmetrical dienophile dimethyl acetylenedicarboxylate (DMAD), in view of minimizing regioselect-ivity problems (Scheme 28). 

Poly(arylene ether triazole)s have also been prepared by heterocyclic-activated displacement polymerization [36], The 1,2,4-triazole unit sufficiently activated, albeit weakly, aryl fluorides for nucleophilic displacement. Several 3,5-bis(4-fluorophenyl)-4-aryl-l,2,4-triazoles were polymerized with various bis-phenols to yield polymers with Tgs from 185 to 230 °C [36]. The 1,2,4-triazole unit appears to be one of the more weakly activating heterocycles towards nucleophilic substitution polymerization. 

The dinuclear complex [(bpy)2Ru(bpt)Ir(ppy)2]2+ was reported by Haas-noot et al., Fig. 22b [ 124], In this complex the two metal centers are linked via a bpt bridging ligand containing a mono anionic triazole unit. Because of this electronic feature, the MLCT states localized on the two moieties involve the peripheral ligands and not the bridging ligand. In [(bpy)2Ru(bpt)Ir(ppy)2]2+, emission is only observed from the Ru-based unit and the direction of intercomponent energy transfer is Ir - Ru, i.e., in the opposite direction from that observed for [(bpy)2Ru(HAT)Ir(ppy)2]3+. 

A library of glycoconjugate benzenesulfonamides that contain carbohydrate-triazole units has been evaluated for their ability to inhibit three human transmembrane carbonic anhy-drase isoz5mies hCA IX, hCA XII and hCA XIV which have potential as dmg targets OFig. 73 [118]. 

By means of the click reaction compounds containing a 1,2,3-triazole unit (5, 6°) have been prepared. 

Triazole-linked glycopeptides are relatively a new class of neoglycopeptides that incorporate the triazole unit via click chemistry hy applying the copper (I)-catalyzed 1,2,3-triazole. Click chemistry has emerged as a new strategy for the rapid and efficient assembly of molecules with diverse functionalities. Among these reactions is the copper (I)-catalyzed 1,2,3-triazole synthesis. It guarantees a reliable synthesis of 1,4-disubstituted... 

Monomers containing the triazole unit are shown in Figure 9.1. The synthetic routes to get 1,2,3-triazole compounds are reviewed in the literature. ... 

Polymers with triazole groups act to enhance the electroluminescent efficiency when used in two layer devices with PPV as a hole-transporting emitter. PPV-hased copolymers bearing an electron-withdrawing triazole unit in the main chain can be synthesized by the Wittig reaction between triazole diphosphonium salt and the corresponding dialdehyde monomers, respectively. ... 

TAZ, c.f. Figure 9.5, is a low electron mobility material. It can be used as a hole blocking layer, which may limit electron injection and transfer in electroluminescent devices. The triazole unit was found to be an effective r-conjugation interrupter and can play the rigid spacer role in determining the emission color of the resulting copolymer. ... 

Monomer reactivity ratios with various comonomers are summarized in Table 9.2. For all comonomers, the methacrylate tends to form blocks repeated by a single 1-vinyl-1,2,4-triazole unit. 

Similarly, poly(vinylbenzylchloride) was produced by free radical polymerization of 4-vinyl-benzylchloride and funchonalized with 3-amino-1, 2,4-triazole and IH-1,2,4-triazole [99], The polymers were doped with trifiuoromethanesulfonic acid at different molar ratios from 0.5 to 3 with respect to the aminotriazole and the triazole units. The samples are thermally stable up to approximately 200 °C. 

Potrekar RA, Kulkami MP, Kulkarni RA, Vemekar SP. Polybenzimidazoles tethered with Wphenyl 1,2,4-triazole units as polymer electrolytes for fuel cells. J Polym Sci Part A Polym Chem 2009 47(9) 2289-303. 

A highly enantioselective catalyst system for the intermolecular (4 -I- 2) cycloaddition of allenamides and dienes was recently disclosed by Ferndndez and coworkers (Scheme 3.77) [108]. The NHC-Au complex featuring a triazole unit embedded in a rigid axially chiral cyclic frame 121 was used as the catalyst for this transformation. The desired optically active cyclohexene products, which are not easily accessible using other methodologies, were obtained in moderate to good yields (48-88% yields) and excellent enantioselectivities (87 to >99% ee s). 

The last discussed gold-catalyzed asymmetric reaction is the asymmetric Diels-Alder reaction of allenamides and dienes, which has been reported by Fer-ndndez and coworkers (see Scheme 9.33) [61]. The reaction is catalyzed by a chiral enantiopure gold complex bearing the chiral NHC ligand shown in Scheme 9.32. This new ligand family contains a triazole unit that is embedded in... 

Figure 9.6 Some medicinally relevant molecules containing the 1,2,3-triazole unit (this unit in fact is a robust, nonhydrolytically cleavable amide isostere) [48].

Attempts at transforming the triazole unit to the corresponding triazolium derivative proved difficult [60]. 

S-2 for PPARa and PPARy over its / -enantiomer, since only in the former is the triazole unit correctly orientated spatially towards the His449 imidazole unit. 

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