Cyclic acylpalladation

Cyclic acylpalladation. Another major subtopic of carbopalladation is acylpalladation. In the mid-1960s, two seemingly independent papers were published by J. Tsuji [24] and P.R. Hughes [25,26]. The former reported a perfectly alternating copolymerization of norbornadiene with CO (Scheme 8), while the latter described two related Pd-catalyzed carbonylation cyclizations shown in Scheme 9. 

Although the Pd-catalyzed alkene-CO copolymerization reaction must involve a series of acylpalladation reactions, it is outside the scope of this chapter. And, the readers are referred to recent reviews and pertinent references cited therein [27-29]. As such, the cyclic carbonylation reactions of dienes were of limited synthetic utility because of difficulties in controlling regiochemistry and other aspects of importance in fine chemicals synthesis. Whatever the reasons might have been, little had been reported further until the 1980s. 

Development of cyclic acylpalladation of halodienes and haloarylalkenes during the 1983-1985 period [10,30] (Scheme 10) proved to be a breakthrough triggering many subsequent investigations both by the authors group and by others including W. Oppolzer, R. Grigg, and K. Yamamoto. The two discrete cyclic acypalladation reactions shown in Eqs. 1 and 2 of Scheme 10 have been conveniently termed Type I and Type II cyclic acyl-... 

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-... 

Table 1 Effect of ring size ont he competition between cyclic carbopalladation and cyclic acylpalladation in the presence of CO...

Ring size Substrate Cyclic carbopalladation Cyclic acylpalladation... 

All of the examples of trapping of acylpalladium species with enolates discussed above as part of the Type III Ac-Pd process involve trapping with O-enolates. As discussed earlier, however, acylpalladium derivatives can also be trapped with C-enolates (Eqs. 4 and 5 in Scheme 11), and this trapping with C-enolates has since been exploited for terminating acyclic carbopalla-dation process [135] (Scheme 48). However, this process does not appear to have been used for terminating cyclic acylpalladation processes. 

Double or Multiple Carbopalladative Cyclization Reactions Involving One or More Cyclic Acylpalladation Processes... 

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. 

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