Addition substituting, with migration

In general, Pd-catalyzed allylic substitutions with soft nucleophiles involve nudeophilic attack directly on the allyl unit, on the opposite face to that occupied by the metal. This is contrasted with the situation for hard nucleophiles where the initial attack occurs at the metal, with subsequent migration of the nudeo-phile to the allyl moiety - the addition to the allyl unit therefore occurring from the same face as the metal. Obviously, this has profound implications on the stereochemical outcome. 

Redox and homolytic substitution reactions almost never directly form C—C, C—N and C—O bonds. Such bonds are generated in radical addition reactions (Scheme 14). Intermolecular addition reactions are presented in this chapter. Cyclization reactions have important similarities with, and differences from, bimolecular additions, and they are presented in Chapter 4.2 of this volume. Falling under the umbrella of addition reactions are radical eliminations (the reverse of addition) and radical migrations (which are usually, but not always, comprised of an addition and an elimination). 

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