Dearomatization Catalyzed by Palladium, Iridium, and Related Complexes

2 Dearomatization Catalyzed by Palladium, Iridium, and Related Complexes 

Sevaal metal-catalyzed dearomatization sequences have been developed that rely upon the electro-phUicity of jt-aUyl metal complexes to initiate carbon-carbon bond formation with arene nucleophiles. When alkylation of jt-aUyl metal intemediates takes place at a substituted arene carbon, then a quatonaiy centCT is genCTated, thCTcby preventing subsequent rearomatization. Ranote electron-donating substituents (such as phenohc residues) help to increase and direct the reactivity of arene substrates in these transformations. 

Allyl complexes of palladium and iridium are conveniently generated by oxidative addition between Pd(0) and Ir(I) catalysts and allylic acetates and carbonates. Chiral allyl complexes 

SCHEME 15.27 Examples of natural product synthesis featuring metal caibenoid dearomatization, (a) Conversion of arene to cycloheptatriene en route to harringtonolide [78]. (b) and (c) CoppCT caibenoid cyclopropanation of arenes to give stable norcaiadiene products [79a,b]- 

SCHEME 15.28 Pd- and Ir-catalyzed asymmetric dearomatization via (allyl)metal intermediates. 

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