Issue Date: June 25, 2007
Copper intermediate sighted
After eluding investigators for more than three decades, the predicted copper(III) intermediate at the heart of many synthetically useful organocopper reactions has finally been stabilized and observed, thanks to a rapid-injection NMR spectroscopic technique (J. Am. Chem. Soc. 2007, 129, 7208). Steven H. Bertz, Michael Murphy, Craig A. Ogle, and coworkers at the University of North Carolina, Charlotte, used an NMR tube chilled to -100 oC as their reaction and observation vessel. They first prepared a solution containing the methylating reagent (CH3)2CuLi•LiCl and trimethylsilyl cyanide. When 2-cyclohexenone was injected into this mixture, it was converted almost exclusively into the copper(III) intermediate shown. This species, the chemists find, persists indefinitely at -100 oC, allowing them to characterize it extensively using NMR techniques. Upon warming to -80 oC, the intermediate breaks down to form the expected product, which has a methyl group attached to the ring carbon that formerly carried the copper. A theoretical study by James P. Snyder and Haipeng Hu at Emory University confirms these results (J. Am. Chem. Soc. 2007, 129, 7210).
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © American Chemical Society