Aryl palladium migrations

About the same time that we discovered this aryl to aryl palladium migration chemistry, we observed a similar vinylic to aryl palladium migration process, which readily affords alkylidene fluorenes (Scheme 25).22 In this case,... 

Several different alkyl to aryl palladium migration processes have been also recently discovered using our standard palladium migration conditions (Scheme 28).24 Thus, both intramolecular Heck and intramolecular arylation... 

An extension of this vinylic to aryl palladium migration was reported later using A-aryl-3-iodoaniline, instead of iodobenzene, as the substrate under improved reaction conditions (Scheme 3) to afford 4-vinylcarbazoles [25], For reasons not understood, this reaction is limited to substrates whose N-H bonds are not substituted. Overall, the reaction offers a quick synthetic approach to carbazoles, which involves the... 

Scheme 1 Vinylic to aryl palladium migration in the synthesis of 9-benzylidene-9/f-fluorenes...

Scheme 2 Proposed mechanism for the annulation involving vinylic to aryl palladium migration...

Besides vinylic to aryl migrations, aryl to aryl palladium migrations have also been studied. Although it may seem that the aryl to aryl migration should be a reversible process, which is indeed observed in some cases, reactions of this type may be driven in one direction by introduction of an intramolecular palladium trap to selectively react with the palladium after migration. 

Table 1 Aryl to aryl palladium migration in biphenyls terminated by Heck coupling...

Table 4 Aryl to aryl palladium migration terminated by arylation/insertion3...

Scheme 4 Benzylic to aryl palladium migration and Heck trapping in a naphthalene system...

The first detailed study of alkyl to aryl palladium migrations, reported in 2004, involved homobenzylic to phenyl migration (Table 5) [58], The process was demonstrated using aryl iodides tethered to an olefin. An additional hap, either intramolecular arylation or intermolecular Heck olefination, was used to hap the migrated palladium. The reaction gives high yields of the desired polycyclic products. 

Scheme 15 1,5-Vinylic to aryl palladium migration in a Sti lie coupling involving a direct proton transfer...

The aryl to aryl palladium migration has been studied computationally on a variety of systems, ranging from 1,3-migration to l,°°-migration [31]. The energetically favored process for each reaction system is summarized in Table 9. Somewhat... 

Table 9 Energetically favored pathways for different types of aryl to aryl palladium migrations...

Zhao, J. and Larock, R.C. (2(K)5) Synthesis of substituted carbazoles by a vinylic to aryl palladium migration involving domino C—H activation processes. Org. Lett., 1, 701. ... 

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