Multiple Heck 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 

For good yields in such vicinal multifold couplings, it may be essential to use the protocol of Jeffery [100,101]. When this is done, the three- and even fourfold vicinal couplings of oligohaloarenes can be achieved without problems [141, 194b,d]. 

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Multiple Heck Couplings of Oligohaloarenes with Alkenes 312... 

C. MULTIPLE HECK COUPLINGS OF 1 -DIBROMOCYCLOALKENES AND RELATED COMPOUNDS... 

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. 

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)... 

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. 

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