Copper catalysts aqueous media reactions

The reaction proceeds in aqueous medium at 0°C, preferably with copper(I) chloride as catalyst. 

From the environmental and economical viewpoints, water is the ideal green solvent for both the synthesis of coordination compounds and the catalytic transformations of organic molecules including the oxidative functionalization of alkanes [23]. However, the performance of catalytic reactions in aqueous medium typically requires the use of hydrosoluble catalysts that often mimic the functions of enzymes. Although various bioinspired multicopper complexes were synthesized as models of pMMO and related copper-based enzymes [3-5a], those catalysts were often not soluble in water, exhibited modest activities, or were almost not tested in oxidative transformations wherein alkanes are used as substrates. 

Direct enantioselective addition of terminal acetylenes to Meldrum s acid-derived acceptors promoted by Cu catalysts have been the subject of investigations by Carreira (Equation 39) [158], The process utilizes the aminophos-phine ligand N-PINAP (210), a member of a family of modular and easily synthesized QUINAP (212) analogues [159], A wide range of Meldrum s acid-derived acceptors such as 209 have been shown to participate in addition reactions of aryl acetylenes, as exemplified by the isolation of 211 in 94% yield and 95 % ee [158]. The process, in which an acetylide is generated in situ in an aqueous medium under mild conditions, owes its success to the ability of terminal acetylenes to undergo metalation in the presence of copper. 

Copper is commonly used as a catalyst for a variety of organic reactions applying organometallic intermediates (114,115, 148-150). These processes include the Ullmann reaction, the Sandmeyer reaction, the Meerwein reaction, the Click reaction, a variety of atom transfer processes including pol5maerizations, etc. Many of these processes involve radicals and redox processes initiated by the copper species. All these processes are usually carried out in aprotic solvents and are therefore beyond the scope of this review. However, the mechanism of some of them was studied in aqueous solutions with the hope to perform them in this medium and in order of determining their detailed mechanisms. 

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