Oxidation of aromatic alkynes with nitrate radicals (NO3 •): An experimental and computational study on a synthetically highly versatile radical

Abstract

Addition of electro- and photochemically generated nitrate radicals, NO3?, to the C?C triple bond of aromatic alkynes 9a?9h leads to formation of 1,2-diketones 10a?10h. Surprisingly, benzophenones 11a?11h are obtained as by-products, which formally result from loss of a carbon atom. Density functional studies performed with the BHandHLYP method in combination with various basis sets revealed that 1,2-diketones result from 5-endo cyclization of the initially formed vinyl radical and loss of NO?. The key step to benzophenone formation is a ?-cleavage at the stage of the vinyl radical with release of NO2?, followed by Wolff rearrangement of the resulting ?-oxo carbene. © CSIRO 2007.