Dienes nonconjugated, double-bond migration

Nonconjugated dienes and polyenes undergo double-bond migration to form the most stable conjugated system in the presence of basic catalysts. Dienes in which the two double bonds are separated by only one carbon atom exhibit the highest reactivity. Double-bond shifts in dienes with more separated double bonds take place in consecutive steps under catalytic conditions that is, only the monoanion is formed.122... 

Vinylation of heteroaryl triflates also possible. Vinyl halides can be coupled to alkenes to form dienes. " The reaction of dihydrofurans with vinyl triilates and a palladium catalyst leads to a nonconjugated diene, 33. This example illustrates that the product is formed by an elimination step, as with the Heck reaction (13-10), and double bond migration can occur resulting in allylic rearrangement. 

The initial stage involves the formation of a highly reactive anion Fe(CO)4 , which interacts with isolated double bonds, followed by double bond isomerization and the formation of n-complexes with the iron tricarbonyl residues. The final product is composed of the ri" -(butadienyl)irontricarbonyl units with both trans-trans- and cis-trans-tetramethylene groups. Since the iron tricarbonyl complexes with two noncon-jugated double bonds are unstable, no complexes between two polymer chains are formed. The reaction of iron carbonyls with low-molecular-weight nonconjugated dienes is accompanied by the double bond migration. 

Fe(CO)5 isomerizes simple olefins, nonconjugated dienes to conjugated dienes, and it can also catalyze the migration of both double bonds in a conjugated diene to give a new conjugated diene. An attractive mechanism for the isomerizations involves 7r-allyliron hydrides ... 

Aryl halides, nonconjugated dienes, and stabilized enolates can be coupled in high yields. Apparently, this process consists of an addition of an arylpalladium halide intermediate to the less hindered C,C double bond, palladium migration by a sequence of /3-hydride elimination, and readdition steps with eventual formation of a Tr-allylpalladium complex and its coupling with a nucleophile (Scheme... 

At this point, it is interesting to note that nonconjugated dienes react first with one double bond and the rr-allyl complex is formed by migration of the other double bond (Scheme This three-component reaction can be carried out with a full range of... 

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