Carbopalladation alkene termination

Cascade carbopalladation sequences after attack on an alkene are most commonly terminated by dehydropallada-tion, if a / -hydride is available in a yy//-orientation. The intramolecular carbopalladation starting from the monocyclic diene 122 with a geminally disubstituted alkene terminator leads to a neopentylpalladium intermediate 123, which cannot undergo /J-dehydropalladation, but continue the cascade by a carbopalladation to eventually form the... 

Negishi E, Coperet C (2002) Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1431... 

D.i.a. Formation of Cyclopropane Derivatives by Two Successive Intramolecular Carbopalladations. Intramolecular carbopalladation starting from 1,( —l)-dienes with a suitable leaving group at the 2-position and a substituent at the (n-l)-position of the alkene terminator leads to a neopentylpalladium intermediate, which can only continue the cascade by a 3-eJto-tng-carbopalladation to eventually form bicyclo[(n—2). 1.0]alkenes. This sequence works equally well for ring sizes five, six, and seven in the first formed ring (Scheme 22) and even heterocyclic systems can be constructed by this mode (Scheme 22). 

IV.3.3 Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions... 

In principle, carbonylative cyclization, that is, acylpalladation or Ac—Pd process, or noncarbonylative cyclization, that is, sample carbopalladation or C—Pd process, in the presence of CO and a Pd catalyst. Various possibilities with halo alkenes as representative substrates are shown in Scheme 2P Those processes that incorporate CO in the cyclization processes are discussed in Part VI including Sects. VI.4-VI.6. hi this section, those cases that do not incorporate CO during the cychzation processes but do so only after cyclization will be discussed. Such cychc carbopalladation-carbonylative termination tandem and cascade processes are represented by the Type II C—Pd process in Scheme 2, which may take place in competition with the other processes shown in Scheme 2, especially the cyclic Heck reaction (Type 1 C—Pd process) and cyclic carbopalladation involving cyclopropa-nation (Type 111 C— Pd process). 

C. Pd-CATALYZED TANDEM AND CASCADE CARBOPALLADATION OF ALKENES TERMINATED BY CARBONYLATION... 

Disubstituted alkenes and other alkenes that can undergo living carbopalladation (e.g., norbomene) can participate in the carbopalladation-carbonylative termination... 

With 1,1-disubstituted alkenes, diastereoselective and/or enantioselective cycUc carbopalladation can, in principle, be achieved. Whereas the latter has not yet been demonstrated for the cyclic carbopalladation-carbonylative termination processes, its diastereoselective version promises to provide an attractive method for the synthesis of chiral natural products. 

For such cascades with intramolecular carbopalladations, smaller ring sizes (5 and 6) are preferred due to the entropic term thus, 1,1-disubstituted alkenes suitably located in the substrate preferably serve as the relay without formation of the larger ring size resulting from insertion into the terminal alkene moiety. 

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