Addition reactions to dienes

Despite the enormous importance of dienes as monomers in the polymer field, the use of radical addition reactions to dienes for synthetic purposes has been rather limited. This is in contrast to the significant advances radical based synthetic methodology has witnessed in recent years. The major problems with the synthetic use of radical addition reactions to polyenes are a consequence of the nature of radical processes in general. Most synthetically useful radical reactions are chain reactions. In its most simple form, the radical chain consists of only two chain-carrying steps as shown in Scheme 1 for the addition of reagent R—X to a substituted polyene. In the first of these steps, addition of radical R. (1) to the polyene results in the formation of adduct polyenyl radical 2, in which the unpaired spin density is delocalized over several centers. In the second step, reaction of 2 with reagent R—X leads to the regeneration of radical 1 and the formation of addition products 3a and 3b. Radical 2 can also react with a second molecule of diene which leads to the formation of polyene telomers. 

Conjugation leads to the formation of allyl systems in addition reactions to dienes, and is a requirement for the Diels-Alder reaction (Fig. 12.84). 

Nucleophilic addition reactions to dienes provide a facile synthesis to chelating 77 r7 -ligands. Several examples have been commented upon in Section 9.2.2 (see Scheme 8), particularly remarkable being the nucleophilic addition of the... 

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