Unusual Radical Acceptors

This article deals with three particular classes of unusual radical traps, i.e. azides, isonitriles, and heterocumulenes. It aims at showing that not only are those compounds easily accessible and much more stable and hazard-free than expected, contrary to many prejudices, but they allow outstanding radical synthetic procedures that can give access to an extensive assortment of compounds. Azides are easy-to-make, extraordinarily versatile products for assembly of both cyclic and acyclic nitrogen compounds through the intermediacy of a variety of nitrogen-centered radicals (triazenyl, aminyl and even iminyl radicals). Likewise, isonitriles are key intermediates for the synthesis of assorted nitrogen heterocycles and other remarkable derivatives via generation of imidoyl radicals, often through multi-component procedures. Even the more unusual heterocumulenes have shown their potential in free-radical-mediated organic synthesis, especially as a route to cyclic and polycyclic compounds. The employment of the above moieties as radical acceptors in organic synthesis shows once more that radical reactions can be applied to a really huge range of substrates and are definitely one of the most widespread tools in organic chemists' hands.