Methylene-7r-allylpalladiums

Reactive methylene-7r-allylpalladiums 618 are generated from esters of 2,3-aUca-dienyl alcohols 617, and react with nucleophiles to afford either 1,2-dienes 619 or 1,3-dienes 620 regioselectively depending on the nature of allyl leaving groups and nucleophiles. 

Hayashi found that methylene-7r-allylpalladium 635 can be generated from 2-bromo-1,3-diene, which is prepared by the Pd-catalyzed cross-coupling of 1,1-dibromo-l-alkene 633 with vinylzinc reagent. Thus, the reaction of l-phenyl-2-... 

Leighton constructed the complex molecule of the CP-263,114 core ring system 641 by elegant application of Pd-catalyzed carbonylation of the 1,3-butadienyl 2-triflate moiety in 637 via the methylene-7r-allylpalladium 638 to afford the unsaturated lactone 640. The lactone was subjected to Cope rearrangement to produce 641 as shown by 640 in 56 % overall yield. Formation of the unsaturated lactone 640 by intramolecular acetalization involving the alcohol, ketone, and acylpalla-dium as shown by 639, is a key reaction [228]. 

Facile Pd(0)-catalyzed reactions of 2,3-alkadienyl derivatives 59 with nucleophiles occur via the formation of methylene- 7r-allylpalladium intermediates 60, from which 1,2- and 1,3-dienes 61 and 62 are formed depending on the nature of the pronucleophiles. These reactions are treated in Chapter 4.11. 

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