Multicomponent Click Synthesis of 1,2,3-Triazoles in Water Catalyzed by New Copper(II) Complex

1,2,3-Triazoles are prevalent building blocks of several classes of nitrogen-containing heterocyclic compounds and are commonly employed as a powerful tool in many fields of chemistry such as pharmaceuticals, agrochemicals, dyes and materials. Recently, the catalytic preparation of 1,2,3-triazoles in the presence of transition metal ions, such as Zn, Cu, Ru, Pd, Ce etc., has been developed. Among these, the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reactions have attracted much attention due to their exclusive regioselectivity, wide substrate scope, mild reaction conditions and high yields [1]. β-Hydroxytriazoles are increasingly useful and important materials in drugs and pharmaceuticals. So, development of a simple and efficient method for their synthesis in a single-step operation is one of the attractive research fields in synthetic organic chemistry. The ability of epoxides to undergo ring opening and hence bringing out the structural diversity in target molecules has made them interesting contenders for in situ azide generation in CuAAC reactions [2]. Nucleophilic addition to epoxides plays a pivotal role in the stereoselective preparation of 1,2-disubstituted products and it has been certainly the most thoroughly studied reaction. It must be highlighted that the multicomponent synthesis of hydroxytriazoles catalyzed by Cu-catalysts is regiospecific with regard to both the azidolysis of the epoxide and the 1,3-dipolar cycloaddition of the in situ generated azidoalcohols with terminal alkynes [3]. In this research we report synthesis, characterization and spectroscopic properties of a new copper(II) complex obtained from the reaction of Cu(NO3)2∙3H2O and 1,3-oxazolidine based ligand in methanol solvent. The obtained Cu(II) complex was used as a catalyst for the green click synthesis of β-hydroxytriazoles in water solvent. Since temperature has considerable effects on the regiospecific opening of the epoxide rings, the effect of temperature was also studied. For this propose, the cycloaddition reaction was studied at 25 (room temperature),40, 50, 60, 70, 80 and 100 ᵒC. The results indicated that increasing the reaction temperature from 25 to 40 and 50 ᵒC increased the catalytic reactivity of copper complex. Further increasing the temperature to 60, 70, 80 and 100 ᵒC also decreased the reaction time but at these temperatures one other product was also obtained. At 100 ᵒC, the ratio of the two products was approximately equal (50 : 50).