Intramolecular Reactions with Alkenes and Alkynes

In contrast to a facile intermolecular insertion of alkenes and alkynes to Pd-aryl and Pd-alkenyl bonds as observed in Heck reaction, curiously intermolecular insertion of alkenes and alkynes to Pd-allyl bond in 7r-allylpalladium is very rare. On the other hand, intramolecular insertion of alkenes and alkynes to r-allylpalladium occurs smoothly to form five- and six-membered rings. Oppolzer and co-workers have developed a useful synthetic method of cyclic compounds by intramolecular insertions of alkenes and alkynes, and they explained the reaction as Pd-ene reaction as shown by 404. The method has been applied to the syntheses of several natural products and complex cyclic compounds [155,156]. 

Efficient domino cyclization of the allyl acetate bearing an allene moiety 409 under CO in AcOH afforded the tetracyclic diketone 413 [158]. The first step is the attack of the tt-allyl group at the central carbon of the allene to form 410 (or insertion of one of the allene double bonds), which is a stable 7r-allylpalladium 411. Then domino insertion of double bond, CO, double bond, CO, and double 

Backvall and co-workers observed that intramolecular reaction of allyl group with allene in 414 (415 to 416) proceeded stereoselectively by an anti attack of allene on 7r-allylpalladium, generated from cyclic cw-allylic pivalate 414. Overall retention occurred in the cyclization to afford 417. Thus, cyclizations of cw-pivalate 414 and trans-pivalalQ 418 afforded cis and trans products 417 and 419, respectively [159]. 

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