Cascade carbopalladation allene termination

F.i.a. Soft Nucleophiles. As mentioned before, dialkyl malonate enolates are useful terminators for cascade carbopalladations, leading eventually to rr-allylpalladium intermediates. This has been demonstrated by Ma and Negishi in their studies regarding allenes as relays for medium- to large-ring synthesis (Scheme... 

The Pd(OAc)2/dppb-catalyzed cascade reaction of o-iodophenol with 1,2-nonadiene and CO starts with a CO insertion which is followed by carbopalladation of the allene and subsequently terminated by an intramolecular nucleophilic substitution to afford O-con-taining six-membered a-methylenebenzo-y-dihydropyrones (Scheme 34). ... 

Domino or cascade reactions provide valuable approaches, especially to various carbo- and heterocyclic systems with three, four, or even more annelated rings. The Heck reaction has successfully been employed in various inter-inter-, intra-inter-, inter-intra-, as well as all-intramolecular reaction cascades, hi this section, the termination of these processes by alkenes, arenes, and related ir-bond systems such as alkynes and allenes will be described. A cascade Heck reaction is considered to consist of an oxidative addition of a heteroatom-carbon bond to palladium (starter), carbopalladation of a nonaromatic carbon-carbon double or triple bond without immediate dehydropalladation (relay), one, two, or more fimher car-bopalladation(s) of a carbon-carbon double or triple bond, and eventually ensuing dehydropalladation. Crucial for a cascade reaction of this kind to occur is the blockage or retardation of a dehydropalladation at one of the intermediate stages by using 1,1-disubsti-tuted alkenes and appropriately substimted cycloalkenes, bicycloalkenes, or alkynes as relays since they give kinetically stable alkyl- or alkenylpalladium intermediates, respectively. 

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