Recent Trends and Prospects in the Copper‐Catalysed “on Water” Reactions

Abstract

Recalling the serious hazards imposed by the “ungreen” techniques used over the years, chemists are now expected to adopt synthetic tactics that strictly adhere to the three E's of green chemistry: Environmental, Economical and Energy efficient. Among the various measures undertaken to improve the benignity of a chemical system, top priority has been given for identifying abundant, non‐toxic and non‐flammable greener solvents such as water, replacing detrimental organic solvents. Despite the safer aspects, reactions in aqueous solutions hardly meet the green chemical standards, particularly due to the challenging product isolation and purification techniques. Sharpless's demonstration of, until then almost unknown, “on water” effect was a major breakthrough in the realm of sustainable organic chemistry. Needless to say, integration of homo‐/heterogeneous water‐compatible catalysts under “on water” conditions without deteriorating its efficiency, has also awakened the industrial prospects of the protocol. Among the various transition metals, copper complexes or salts are considered as first line catalysts due to their irrevocable contributions to the synthetic world. Also, due to the water tuneable nature of these catalysts, many copper‐catalysed organic transformations that once required harsh conditions, could now be obtained using clean and safe protocols. This review comprehends the recent advancements in the copper‐catalysed “on water” reactions covering literatures since 2006.

Metal-Catalyst-Free Radical Cyclization of 1,6-Enynes for the Selective and Switchable Synthesis of Lactams in Water

“…The commonly used organic solvents are generally volatile and toxic, so it is a sustainable choice to find environmentally friendly media as an alternative. − As the greenest and safest solvent in nature, water has drawn the attention of chemists due to its excellent biocompatibility, nonflammability, and nontoxicity. − Hence, it is of great significance to exploit organic reactions in aqueous media. In addition, the development of the metal-catalyst-free method is also booming due to its low toxicity, long service life, and simple postprocessing. − Inspired by these advances and as a continuation of our efforts in radical cyclization of unsaturated hydrocarbons, − we present a sustainable and switchable radical cyclization of 1, n -enynes with sulfonyl hydrazines in aqueous media without a metal catalyst to form five-membered cyclic lactams, five-membered cyclic lactams containing C–I bond, and six-membered cyclic lactams (Scheme -2).…”

Synthesis and Antimicrobial Activity of the Pathogenic E. coli Strains of p-Quinols: Additive Effects of Copper-Catalyzed Addition of Aryl Boronic Acid to Benzoquinones

“…Additionally, the formation of side products hampered product purification. Therefore, the previously developed method is characterized by low atom economy [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ].…”

Copper Catalyzed Synthesis of Heterocyclic Molecules via C–N and C–O Bond Formation under Microwaves: A Mini-Review

“…Later on, Buchwald and Hartwig groups demonstrated the Pd catalyzed C–N bond formation reaction. Of late the Chan and Lam group achieved a major breakthrough on the Cu-catalyzed C–N bond formation reactions. , It has been noticed that other than palladium or copper, several other transition metals such as nickel, zinc, iron, cobalt, and manganese are also used for C–N and C–O bond forming reactions . However, all those methods suffer various drawbacks such as the high reaction temperature, use of costly ligands, lack of substrate scope, and lots of waste generation, etc.…”