Cascade carbopalladation, intra-intermolecular

Grigg and Xu have developed a variety of so-called queuing cascades involving allenes. The intra-intermolecular carbopalladation sequence of the <9-iodo-A-methyl-A -(methylallyl)aniline 142 and 1,1-dimethylallene 143 with subsequent / -dehydropalladation leads to the 1,3-dienyl-substituted indole derivative 144, which is immediately trapped by an added dienophile (e.g., A-methylmaleimide) in a Diels-Alder reaction to yield 145 (Scheme 37)7 ... 

When the ort/io-alkynyl tether on the iodoarene bears a terminal aryl group the cascade process after the intra-intermolecular carbopalladation sequence may be terminated by an ortho attack of the norbomylpaUadium intermediate on the previously terminal aryl group (cf. Scheme 10) to yield an oligocyclic system (Scheme... 

Selective synthesis of benzene derivatives via partially intramolecular cyclic carbopalladation is considerably more complex than the corresponding all-intramolecular processes. As it is generally difficult to specify the cascade-initiation point in the Type Ha cyclization process, it would generally be the least selective path. A priori, the most favorable might be the intra-inter cascade cyclization process (Type lib), since both the point of initiation and the queuing order between the two alkynes is sharply differentiated by the fact that one is intramolecular, while the other is intermolecular. Still, in-... 

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