Issue Date: November 17, 2008
Grignard Radical Ensnared
A key radical intermediate in the Grignard reaction, a textbook reaction in organic synthesis, has been trapped and studied for the first time (Angew. Chem. Int. Ed. 2008, 47, 9118). The organomagnesium Grignard reagent generally reacts with a carbonyl compound to form an alcohol. Normally it acts as a nucleophile, but sometimes a radical mechanism is involved. Despite the reaction's broad use, researchers have never observed the presumed intermediate along the radical pathway, a magnesium ketyl radical. Richard A. J. O'Hair's team at the University of Melbourne, in Australia, managed to snag the intermediate in the gas phase. The team first formed the radical anion MgCl2·¯ in a mass spectrometer. They then reacted MgCl2·¯ with ketones to trap the intermediate and study its reactivity. Their results suggest that the ketyl radical plays a role in forming side products in some Grignard reactions. As a new radical reagent, MgCl2·¯ could aid studies of myriad organic and biological reactions, University of Utah professor and mass spectrometry expert Peter B. Armentrout notes.
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