Oxidation of aromatic alkynes with nitrate radicals (NO3 center dot): An experimental and computational study on a synthetically highly versatile radical (vol 60, pg 420, 2007)

摘要

Addition of electro- and photochemically generated nitrate radicals, NO3 center dot, 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 center dot. The key step to benzophenone formation is a gamma-cleavage at the stage of the vinyl radical with release of NO2 center dot, followed by Wolff rearrangement of the resulting alpha-oxo carbene.