Organopalladium carbopalladation

The palladium(0)-catalyzed cyclization of amide-allenes via a carbopalladation has been developed by several groups. The reaction proceeds through the carbopalladation of the allene moiety with an organopalladium species (R-Pd-X), generated by oxidative addition of R-X to palladium(O), and subsequent reductive elimination of the resultant 7r-allylpalladium intermediate.47,47a 47f... 

Termination of cascade carbopalladation sequences by arylation can play a major role in systems that form a reasonably long-lived palladium intermediate and contain a suitably functionalized arene moiety in the vicinity of the organopalladium function. In particular, neopentylpalladium intermediates have been found to intramolecularly attack an adjacent arene moiety. For example, iodoarenes 149 with electron-withdrawing substituents in the... 

Carbopalladation occurs with soft carbon nucleophiles. The PdCl2 complex of COD (100) is difficult to dissolve in organic solvents. However, when a heterogeneous mixture of the complex, malonate and Na2C03 in ether is stirred at room temperature, the new complex 101 is formed. This reaction is the first example of C—C bond formation and carbopalladation in the history of organopalladium chemistry. The double bond becomes electron deficient by the coordination of Pd(II), and attack of the carbon nucleophile becomes possible. The Pd-carbon n-bond in complex 101 is stabilized by coordination of the remaining alkene. The carbanion is generated by treatment of 101 with a base, and the cyclopropane 102 is formed by intramolecular nucleophilic attack. Overall, the cyclopropanation occurs by attack of the carbanion twice on the alkenic bond activated by Pd(II). The bicyclo[3.3.0]octane 103 was obtained by intermolecular attack of malonate on the complex 101 [11]. 

Since both starting organometals and products in carbopalladation are organopalladium derivatives (Schemes 1 and 2), the process of carbopalladation can, in principle, repeat itself as exemplified in the reaction shown in Scheme 4. Thus, unless intercepted by some C - Pd bond cleaving process, this living process will stay alive, and no catalytic process will result. In both Heck and Maitlis reactions, the carbopalladation steps are spontaneously followed by /1-dehydropalladation and dechloropalladation, respectively. In cases where no such process occurs spontaneously, some processes must be deliberately devised usually through addition of appropriate reagents. In addition to dehydropalladation and dechloropalladation shown in Schemes 3 and 4 as well as in Eqs. 1 and 2 in Scheme 5, several other reactions used for this purpose are exemplied with prototypical cases of catalytic cyclic carbopalladation shown in Scheme 5 [9-19]. 

In addition to a couple of reviews focused on results obtained in the authors group [38,39], a comprehensive book on organopalladium chemistry for organic synthesis [40] contains two dozens or so chapters on cyclic car-bopalladation and cyclic acylpalladation. Thus, its Part IV (pi 123-1659) on carbopalladation contains reviews of cyclic carbopalladation on the synthe-... 

Although this chapter focuses its attention on cyclic carbopalladation reactions other than the cyclic Heck reaction, it might be useful to discuss here the following variants of the cyclic Heck reaction. For the vast topic of the cyclic Heck reaction including those variants discussed below, the reader are referred to the following chapters of the Handbook of Organopalladium Chemistry for Organic Synthesis [40]. 

Kozhushkov SI, de Meijere A (2002) Carbopalladation of Alkenes not Accompanied by Dehydropalladation. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1317... 

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