Issue Date: May 24, 2010
Metal-Free Alkene Dioxygenation
Dioxygenation of alkenes normally requires expensive and sometimes toxic transition-metal catalysts, but Valerie A. Schmidt and Erik J. Alexanian of the University of North Carolina, Chapel Hill, have developed a less costly, metal-free approach to the reaction (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201000843). The technique is “green” in that it uses only O2 or air as an environmentally benign and inexpensive oxidant and oxygen-atom source. In this intramolecular reaction of unsaturated N-aryl hydroxamic acids, the hydroxamic acid is first converted to an amidoxyl radical. The radical then attacks the alkene, and subsequent reaction of the intermediate with O2 delivers the dioxygenated alkene product (shown). The reaction is applicable to a wide range of alkene substrates, with the potential for high levels of stereocontrol, the researchers note. The dioxygenated product further provides access to 1,2-diols by mild reduction of its N–O bond. “Future studies will explore the unique reactivity of amidoxyl radicals in the development of new reactions and in complex synthetic applications,” the researchers write.
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