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 γ-cleavage at the stage of the vinyl radical with release of NO₂^•, followed by Wolff rearrangement of the resulting α-oxo carbene.