Cu-Modified Magnetic Creatine as an Efficient Catalyst for Regioselective Preparation of 1,2,3-Triazoles Derivatives

A New Insight Into The Huisgen Reaction: Heterogeneous Copper Catalyzed Azide-Alkyne Cycloaddition for the Synthesis of 1,4-Disubstituted Triazole (From 2018-2023)

The Huisgen cycloaddition, often referred to as 1,3-Dipolar cycloaddition, is a well-established method for synthesizing 1,4-disubstituted triazoles. Originally conducted under thermal conditions [3+2] cycloaddition reactions were limited by temperature, prolonged reaction time, and regioselectivity. The introduction of copper catalyzed azide-alkyne cycloaddition (CuAAC) revitalized interest, giving rise to the concept of "click chemistry". The CuAAC has emerged as a prominent method for producing 1,2,3-triazole with excellent yields and exceptional regioselectivity even in unfavorable conditions. Copper catalysts conventionally facilitate azide-alkyne cycloadditions, but challenges include instability and recycling issues. In recent years, there has been a growing demand for heterogeneous and porous catalysts in various chemical reactions. Chemists have been more interested in heterogenous catalysts as a result of the difficulties in separating homogenous catalysts from reaction products. These catalysts are favored for their abundant active sites, extensive surface area, easy separation from reaction mixtures, and the ability to be reused. Heterogeneous catalysts have garnered significant attention due to their broad industrial utility, characterized by cost-effectiveness, stability, resistance to thermal degradation, and ease of removal compared to their homogeneous counterparts. The present review covers recent advancements from year 2018 to 2023 in the field of click reactions for obtaining 1,2,3-triazoles through Cu catalyzed 1,3-dipolar azide-alkyne cycloaddition and the properties of the catalyst, reaction conditions such as solvent, temperature, reaction time, and the impact of different heterogeneous copper catalysts on product yield.

Novel Highly Efficient Green and Reusable Cu(II)/Chitosan-Based Catalysts for the Sonogashira, Buchwald, Aldol, and Dipolar Cycloaddition Reactions

In this study, new Cu(II)/chitosan-based systems were designed via (i) the treatment of chitosan with sodium sulfate (1a) or sodium acetate (1b); (ii) the coating of 1a or 2a with a sodium hyaluronate layer (2a and 2b, correspondingly); (iii) the treatment of a cholesterol–chitosan conjugate with sodium sulfate (3a) or sodium acetate (3b); and (iv) the succination of 1a and 1b to afford 4a and 4b or the succination of 2a and 2b to yield 5a and 5b. The catalytic properties of the elaborated systems in various organic transformations were evaluated. The use of copper sulfate as the source of Cu2+ ions results in the formation of nanoparticles, while the use of copper acetate leads to the generation of conventional coarse-grained powder. Cholesterol-containing systems have proven to be highly efficient catalysts for the cross-coupling reactions of different types (e.g., Sonogashira, Buchwald–Hartwig, and Chan–Lam types); succinated systems coated with a layer of hyaluronic acid are promising catalysts for the aldol reaction; systems containing inorganic copper(II) salt nanoparticles are capable of catalyzing the nitrile-oxide-to-nitrile 1,3-dipolar cycloaddition. The elaborated catalytic systems efficiently catalyze the aforementioned reactions in the greenest solvent available, i.e., water, and the processes could be conducted in air. The studied catalytic reactions proceed selectively, and the isolation of the product does not require column chromatography. The product is separated from the catalyst by simple filtration or centrifugation.