Acylpalladation natural product synthesis

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. 

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. 

Despite generally moderate product yields, these reactions have been applied to a number of noteworthy syntheses of natural and unnatural organic compounds of considerable complexity. The synthesis of tetracychc[5.5.5.5]fenestranes by Keese and co-workerst - (Scheme 29) is particularly noteworthy, and it persuasively demonstrates the synthetic utility of the cyclic acylpalladation methodology. A series of elegant syntheses of terpenoids by Oppolzer and co-woikersf f" are discussed later in this section. 

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