Carbopalladation inter-intramolecular cascade carbopalladations

B. INTER-INTRAMOLECULAR CASCADE CARBOPALLADATIONS B.i. Termination by Alkenes... 

Scheme 22 Alkyne relays in inter-intramolecular carbopalladation cascades leading to ring-annelated alkylidenecyclopenta-dienes and cyclopentenes. ...

Scheme 23 Highly convergent assembly of calcitriol 83 employing an alkyne-relayed inter-intramolecular carbopalladation cascade.

An inter-intra-intramolecular carbopalladation cascade, initiated by the alkenylpalladium bromide intermediate from /3-bromostyrene 74 inserting into one of the triple bonds of the diyne 73, yields the ring-annelated fulvene derivative 75 (Scheme 22). ... 

Scheme 37 Two cascade cyclizations involving inter- or intramolecular carbopalladations of allenes.

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-... 

Cascade reactions arising from sequential carbopalladations are especially valuable for the construction of various carbo- and heterooligocyclic systans with three, four, or even more annelated rings. The Heck reaction has successfully been employed in various inter-inter-, intra-inter-, as well as all-intramolecular reaction cascades (Sect. IV.3). In the carbopalladation step of the Heck reaction (Scheme 6) a new metal-carbon bond is formed, which, in principle, can undergo any of the typical reactions of a hydride elimination is not too fast. When the /S-hydride elimination is totally suppressed, the palladium species can undergo a number of reactions with the formation... 

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