Also known as: Ullmann coupling or Ullmann biaryl synthesis
The Ullmann reaction is an organic reaction used to couple two molecules of aryl halide to form a biaryl using copper metal and thermal conditions. The mechanism for the Ullmann reaction is not fully under-stood but there are two popular mechanisms. The radical mechanism begins with a single electron transfer (SET) from the copper metal to the alkyl halide to form an aryl radical. Two aryl radical then react to form the final biaryl product. The second proposed mechanism begins with oxidative addition of the copper to the aryl halide followed by a SET to form an organocuprate reagent. The organocuprate performs another oxidative addition on an aryl halide and after reductive elimination results in the final biaryl product.
Ullmann, F.; Bielecki, J. Ber. Dtsch. Chem. Ges. 1901, 34, 2174–2185.
Ullmann, F. Justus Liebigs Ann. Chem. 1904, 332, 38–81.