Cascade reactions alkene termination

Negishi E, Coperet C (2002) Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1431... 

However, their intermolecular addition reactions with alkynes are mostly aimed at synthesizing substituted aLkenes, ° and only very few cascade reactions that are initiated by P radical addition to C = C triple bonds have been reported. Renaud and coworkers developed a simple one-pot procedure for the cyclization of terminal alkynes mediated by dialkyl phosphites (Scheme 2.35). In this radical chain procedure, dialkyl phosphite radicals, (R0)2P =0, undergo addition to the C = C triple bond in 190, which triggers a radical translocation (l,5-HAT)/5-eAO cyclization cascade. The sequence is terminated by hydrogen transfer from dialkyl phosphite to the intermediate 194 and regeneration of P-centered radicals. 

A cascade Heck reaction with termination by nucleophiles is considered to start with an oxidative addition of a heteroatom-carbon bond (starter) onto a palladium(O) species (startup reaction), followed by carbopalladation of a nonaromatic carbon-carbon double or triple bond without subsequent dehydropalladation (relay), a second and possibly further carbopalladation of a carbon-carbon double or triple bond (second etc. relay). The terminating step is a displacement of the palladium residue by an appropriate nucleophile. It is crucial for a successful cascade carbopalladation that no premature dehydropalladation takes place, and that can be prevented by using alkynes and 1,1-disubstituted alkenes (or certain cycloalkenes) as relay stations since they give kinetically stable alkenyl- or neopentylpalladium intermediates, respectively. In addition, reaction of haloalkenes with alkenes in certain cases may form rr-allyl complexes, which are then trapped by various nucleophiles. 

IV.3.3 Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions... 

Intramolecular Heck reactions leading to carbocycles involving domino, tandem, or cascade reactions terminated with tethered alkenes and other nucleophiles will be covered in Sect. IV.3.1 and V.3.2, respectively. 

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. 

Recently, Dong et al. reported a multicatalytic cascade reaction combining Pd, acid, and Ru catalysis [11]. By coupling palladium-catalyzed oxidation, acid-catalyzed hydrolysis, and ruthenium-catalyzed reduction, the elusive anti-Markovnikov olefin hydration was formally achieved, affording primary alcohols from waters and aryl-substituted terminal alkenes (Scheme 9.8). 

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