Heck reaction multiple couplings

The feasibility of multiple couplings was demonstrated by Heck himself [1, 193]. Such reactions have more recently been improved [194] and further developed to prepare starting... 

Multiple catalyst use. The dramatic decrease in Pd dispersion during the reaction should lead to a significant decrease in catalytic activity, when the catalyst is re-used in the same Heck reaction. This was in fact found in recycling studies with catalyst 3W in Heck couplings of bromobenzene with styrene. The conversion after 6 hours with the recycled methylene chloride washed catalyst is roughly 50 % of fresh 3W. A second recycling of the Pd/C catalyst decreases the reaction rate further and resulted in very low conversion (4 % after 6 hours). For higher or close to complete conversions reaction times of 20 hours or more are necessary. Re-used catalysts exhibit low activities comparable to other (fresh)... 

The field ofi ionic-liquid-stahilized NPs is reviewed Jairton Dupont and D. Dago-herto de Oliveira Silva in Chapter 6, including the supramolecular aspects of ILs (multiple H-bonding) and the most frequent examples of reactions that are catalyzed by IL-stabilized NPs (hydrogenation of olefins, diolefins, arenes and ketones, hydrofor-mylation, Heck reaction and Negishi coupling). 

In this section, a double (or multiple) Heck reaction is defined as a coupling of two (or more) alkene molecules with di- or oligohaloarenes or -alkenes as well as a reaction of two (or more) di- or oligohaloarenes or alkenes with one alkene molecule. 

Cascade Reactions and Multiple Couplings 557 Table 8.7 Examples of ring sizes achieved in intramolecular Heck reactions. 

The multiple coupling of oligohaloarenes with alkenes was described early on by Heck and Nolley in one of their first papers on this new type of palladium-catalyzed cross-coupling reaction. Twofold coupling of 1,4-diiodobenzene with styrene furnished the 1,4-distyrylbenzene in 67% yield, shortly afterward, the double Heck... 

A unique reaction of allenylindium reagents, prepared from propargyl bromides and indium, and haloazines gives rise to the appropriate allenyl-azines. Although the reaction is not a Heck coupling, but a cross-coupling reaction, the aryl moiety is formally attached to a carbon-carbon multiple bond, therefore we mention it here. 

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