Organopalladium complexes in organic synthesis
The reaction of cycloalkenes with chloromethyl carbene followed by dehydrochlorination afforded $\omega$-methylenebicyclo (n.1.0) alkanes. Chloropalladation of the $\omega$-methylenebicyclo (n.1.0) alkanes gave (3-chloro-2-methylenecycloalkyl)palladium chloride dimers. These steps constitute a ring homologation process. Several (3-chloro-2-methylenecycloalkyl)palladium chloride dimers (7-, 8-, 9-, and 11-membered rings $\pi$-allyl; substituted 7-membered ring $\pi$-allyl at position 1, 3, 4, 5, 6, and 7) were synthesized by this method. The (3-chloro-2-methylenecycloalkyl)palladium chloride dimers 24 reacted as either a "trimethylenemethane dication" synthon or an "isoprenyl monocation" synthon with stabilized carbon nucleophiles in the presence of phosphine ligands. The two electrophilic sites of the trimethylenemethane dication synthon are sequentially generated. This reactivity is dependent on the size of the carbocyclic ring, substituents on the ring, the amount and nature of the nucleophile, and the nature of the phosphine ligand. The product 66 from alkylation of two equivalents of malonate anion with (3-chloro-2-methylenecycloheptyl)palladium chloride dimer 34 was cyclized via oxidative coupling to afford the octahydroazulene skeleton. The cyclodialkylation of one equivalent of the dianion of dimethyl 3-ketoglutarate with 34, followed by saponification and decarboxylation, afforded 9-ketobicyclo (5.4.0) undec-1-ene. The reaction of (3-chloro-2-methylenecycloalkyl)palladium chloride dimers 24 with sodium tetraphenylborate proceeds via coupling at either the exocyclic or endocyclic terminus of the $\pi$-allyl to afford phenyl substituted $\pi$-allyl complexes. The regioselectivity of this reaction is somewhat dependent on ring size. The new $\pi$-allyl complexes can further undergo a cleavage reaction or nucleophilic addition. The utility of using these $\pi$-allyl palladium complexes in the synthesis of natural products containing a 5,7 ring system or a 6-7-5 ring system, has been explored.
"Organopalladium complexes in organic synthesis"
(January 1, 1990).
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