Isomerization intramolecular diene coupling

The ruthenium-catalyzed cycloisomerization of a variety of <5-enallenes was also achieved, forming cyclic 1,3-dienes or 1,4-dienes depending on the substrates and reaction conditions [32] (Eq. 22). This intramolecular coupling of the C=C bond and allenes can be envisioned by the initial hydrometallation of the allene moiety followed by intramolecular olefin insertion and isomerization. 

Estrones An A —> BCD approach to estrones involves a cobalt-catalyzed intramolecular [2 + 2 + 2] cycloaddition of the enediyne 1 to form the B, C, and D rings in one step. The high stereoselectivity suggests that the cyclization involves a Diels-Alder-type reaction of the vinyl group with a cobaltacyclopentadiene formed by coupling of the two alkyne units. The homoannular diene obtained on demetalation is isomerized easily to the diene 3. 

Even simple alkenes, such as 1-hexene 9.270, can yield ir-allyl complexes on reaction with vinyl halides under Heck conditions (Scheme 9.75). This is only apparent when a nucleophile is present, such as a secondary amine or a malonate anion. The ir-allyl complex 9.279 is generated by isomerization of the corresponding T -complex 9.278 that is itself generated by a -hydride elimination-reinsertion sequence from the initial insertion product 9.275. Nucleophilic attack on the Tr-allyl complex gives the three component coupling product 9.273, while the Heck product, diene 9.272, can arise from dissociation from t -complex 9.276 or p-hydride elimination from the -intermediate 9.278. Again, the reaction is particularly effective in an intramolecular sense. °°... 

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