Cascade reactions acylpalladation

These reactions may as well occur in the termination stages of cascade reactions, for example, involving intramolecular acylpalladation (Scheme 30) or intramolecular Heck reaction Equation (49). ... 

These allylpalladation-acylpalladation cascade bicyclization reactions have been applied mainly by Oppolzer to the synthesis of various natural products including (zb)-pentalenolactone E methyl ester [152], 3-isorauniti-cine [153], ( )-coriolin [154], and ( )-hirsutene [155]. Their application to the syntheses of [5.5.5.5]fenestrane derivatives by Keese [156,157] (Scheme 63) is also noteworthy. 

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.iLa. Carbopalladation-AcylpaUadation Cascades. The reaction shown at the top of Scheme 30 is a prototypical example of the intra-intra carbopaUadation-acylpalladation cascade, while that shown at the bottom of Scheme 30 is an example of the inter-intra carbopalladation-acylpalladation cascade. 

The synthesis of methylenomycin shown in Scheme 4 represents the first application of cyclic acylpalladation (Type I Ac-Pd process) to the synthesis of natural products. Applications of Ac-Pd reactions to the syntheses of more complex natural products have been made through the use of the cyclic allylpalladation-acylpalladation cascade processes, as indicated by the results shown in Scheme 32. 

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