Triethylaluminum- or Triethylborane-Induced Free Radical Reaction of Alkyl Iodides and α,β-Unsaturated Compounds

A series of α,β-unsaturated compounds, 1a−c, 9, 13, and 17, were used as reactants in free radical conjugate addition reactions with different radicals generated from alkyl iodides such as 3, 4, or 5 in the presence of triethylborane−oxygen in air or via the use of triethylaluminum−benzoyl peroxide as a free radical initiator. When the reactions were carried out using triethylborane−air, the products, in most cases, were clean and were easily purified. However, higher yields of the 1,4-adducts and less side reactions occurred when less reactive substrates were used as Michael acceptors in reactions with triethylaluminum−benzoyl peroxide and alkyl iodide under similar conditions. A mechanism for this is proposed in Scheme .