Greened-Up Copper Addition Reactions

There was once a time when chemists took extra precautions to keep air and moisture out of organometallic reactions, thinking that the reagents were overly sensitive to proton quenching and/or oxidation. But those days are gone. In one of the latest examples, a research team led by Bruce H. Lipshutz of the University of California, Santa Barbara, has created a reaction system to forge new C–C bonds using organocopper chemistry in water at room temperature (J. Am. Chem. Soc., DOI: 10.1021/ja309409e). The researchers take an alkyl halide and an α,β-unsaturated ketone and mix them together with zinc powder, a copper salt, and gold trichloride in water containing TPGS-750-M, a commercial “green” surfactant designed by Lipshutz’ group as part of its effort to avoid using organic solvents. Within the micelles that form, an in situ-generated organozinc intermediate transfers its alkyl group to copper. Copper then completes the task of adding the alkyl group in a 1,4-fashion to an enone substrate, a process assisted by AuCl₃, which serves as a Lewis acid promoter. The micellar system eliminates concerns about the water sensitivity of the organozinc and organocopper reagents, Lipshutz says, plus provides broader reaction scope and higher yields than water-based, radical-induced 1,4-additions studied in the past.