Acylpalladation related carbonylation reactions

Yet another important development in the area of Pd-catalyzed carbonylation is the development of acylpalladation and related carbonyl-Pd bond addition reactions. Acylpal-ladation may be defined as a process of acyl-Pd bond addition to alkenes and alkynes. Clearly, it is a kind of carbopalladation reaction. For practical reasons, however, it is discussed in Part VI together with other carbonylation reactions mentioned above. Tsuji and Hosaka " reported in 1965 what appears to be the first example of the perfectly alternating alkene-CO copolymerization (Scheme 8). Independently, Brewis and Hughes reported also in 1965 a Pd-catalyzed cyclic carbonylation of dienes with CO and methanol (Scheme 9). Although the exact mechanism of the initiation is unclear, these reactions... 

A systematic investigation of cyclic acylpalladation of haloenes, haloynes, and related electrophiles conducted since 1983 [30] has led to the development of three types of cyclic acylpalladation processes (Types I—III Ac-Pd) and Pd-catalyzed carbonylation-induced ketene [2 + 2] cycloaddition (Sect. 3.1). Collectively, these cyclic acylpalladation and related reactions have provided a number of new and attractive routes to cyclic compounds. Significantly, they nicely complement and supplement the non-carbonylative cyclic carbopalladation reactions. Thus, they have become integral and indispensable parts of the carbopalladation-based cyclization methodology. 

As in the cases of termination by lactonization and lactamization, some specially structured alkenes, such as norbomene and related alkenes, can participate in intermolecular carbopalladation-carbonylative ketonization tandem processes. In the reactions shown in Scheme 22, the acylpalladium intermediates undergo intramolecular acylpalladation with arenes to provide ketones. ... 

A related example is also worth noting and involves the reaction of aryl iodides or vinyl triflates with 13 nnder carbonylative conditions to give 14 (43-83% yields) along with small amonnts of 15 (Scheme 24)P This reaction can in principle proceed by either acylpalladation or electrophilic activation of the alkyne moiety. Based on the mechanistic investigation of the noncarbonylative reaction, the electrophilic activation pathway seems to be the most likely mechanism. It is, however, interesting to see that small changes in the substrate can completely change the course of the reaction. 

---