Isomerization intramolecular carbopalladation

The transformations of 136 proceed cleanly upon treatment with a catalytic amount of Pd(PPh3)4, in the presence of triethylamine and molecular sieve (MS) 4 A it apparently is initiated by oxidative addition of the N(sp )-0 bond of 136 to the Pd(0) complex, and this is succeeded by two or even three intramolecular carbopalladations followed by / -hydride elimination. This Heck-type reaction is not affected by the configuration of the oxime derivatives probably due to a facile enough if/Z-isomerization of the alkylideneaminopalladium intermediate. 

Based upon the studies on the mechanism of the Cl sequence we rationalized that the elusive allenol intermediate 19 (Chap. 2.2) could participate in intramolecular trapping reactions as an allenyl ether. Furthermore, vinyl allenes are perfectly suited as dienes in Diels-Alder reactions. Considering both reactive functionalities, allenyl ethers and vinyl allenes, which are perfectly suited for domino processes, we designed an insertion sequence based upon cyclizing carbopalladation [76], where the vinyl aUene results from an isomerization of an alkynylation of a vinyl... 

We reported that the palladium-catalyzed intramolecular cyclization of the A/L(o-alkynylphenyl)-imines 54 gave the 3-alkenylindoles 55 in good to high yields (Scheme 19).100 A hydridopalladium species, generated in situ through the reaction of Pd-(OAc)2, P(n-Bu)3, and H20, reacts with alkynes to produce 56, which undergoes the cycloisomerization via the carbopalladation— -elimination—olefin isomerization. 

Intramolecular reaction of the vinyl triflate with benzo[ ]furan in 7 is a key step in the preparation of the synthetic intermediate 8 of (—)-frondosin A [5], Intramolecular reaction of the iodide with furan in 9 gave the tetracyclic jS-lactam 10 containing furan ring in the presence of TI2CO3 as a base. The rather unusual C-3 substitution occurs in the reactions of 7 and 9, because the C-2 positions are blocked [6], If the cyclizations of 7 and 9 proceed similar to Heck-type carbopalladation and f-H elimination, direct syn y3-H elimination is not possible, and isomerization from anti to syn, followed by syn y3-H elimination should occur. Therefore, direct electrophilic substitution may be a better explanation. 

The Pd(II)-catalysed 5-exo-dig carbocyclization of the alkynyl ketone (49) to produce (50) has been rationalized by DFT calculations, which suggest that the reaction proceeds via enolization assisted by (AcO)2Pd, followed by intramolecular alkyne carbopalladation, Z E isomerization, and protiodepalladation. ... 

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