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Organocopper reagents are widely used in organic synthesis [13]; however, these reagents are typically water sensitive. In 2012, we disclosed a water‐promoted trifluoromethylation of α‐diazo esters to access α‐trifluoromethyl esters, representing the first example of fluoroalkylation of a non‐fluorinated carbene precursor (Scheme 1.1) [14]. We found that “CuCF₃” (prepared from CuI/CsF/TMSCF₃) in n‐methyl‐2‐pyrrolidone (NMP) is stable even in the presence of 66 equiv of water at room temperature within five hours and only about 5% of “CuCF₃” decomposed. Taking advantage of the unusual stability of “CuCF₃” in water (fluorine effect), we could therefore use water (CuI is also applicable) as the iodide scavenger to enhance the activity of “CuCF₃” prepared from CuI/CsF/TMSCF₃ significantly by changing “CuCF₃” in the form of [Cu(CF₃)I]⁻ to “ligandless” [Cu(CF₃)], which is more reactive toward α‐diazo esters. From an organometallic chemistry point of view, water promotes the ligand exchange in “CuCF₃” by eliminating iodide, making the ligation of α‐diazo esters to “CuCF₃” more favorable. The stability of “CuCF₃” toward water and the instability of alkylcopper intermediate 1 toward water ensure the success of this reaction.

Scheme 1.1 Water‐promoted trifluoromethylation.