Cascade reactions allene termination

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. 

Further development of termination strategies has led to the use of allenes, which trap the organopalladium intermediate to give 7r-allylic complex. The latter undergoes facile reactions with nucleophiles. The overall process becomes a pentamolecular cascade (Scheme 17). 

The intra-intermolecular cascade can also be terminated with an external allene, like 1,1-dimethylallene, leading to a 2,3-disubstituted 1,3-diene that can subsequently be trapped by an added dienophile in a Diels-Alder reaction (Scheme 19). ... 

Although less studied than O- and N-nueleophiles, other nueleophilic partners possessing H-X bonds can participate in gold-eatalyzed hydrofunctionalization reactions. Hence, the intermoleeular hydroarylation ie. C(sp2)-H bond addition] of allenes with indoles was reported in the presence of [(IPr) AuCl]. Using the same catalyst, Che and co-workers investigated an interesting cascade terminated by an alkyne hydroarylation step. The intramolecular allene hydroarylation with indoles was also described by Alcaide and Almendros. ... 

---