Palladium-catalyzed/promoted reactions termination

Sakai N, Annaka K, Konakahara T (2004) Palladium-catalyzed coupling reaction of terminal alkynes with aryl iodides in the presence of indium tribromide and its application to a one-pot synthesis of 2-phenylindole. Org Lett 6 1527-1530. doi 10.1021/ol036499u Sakai N, Annaka K, Eujita A, Sato A, Konakahara T (2008) InBr 3-promoted divergent approach to polysubstituted indoles and quinolines from 2-ethynylanilines switch from an intramolecular cyclization to an intermolecular dimerization by a type of terminal substituent group. J Org Chem 73 4160-4165. doi 10.1021/jo800464u... 

A unique system for catalytic silaboration of allenes, in which a catalytic amount of organic halide is used as a crucial additive, has been reported (Equation (86)).232 In the presence of Pd2(dba)3 (5 mol%) with 3-iodo-2-methyl-2-cyclohexen-l-one (10mol%), reactions of terminal allenes with a silylborane afford /3-silylallylboranes in good yields with excellent regioselectivity. It is worth noting that the addition takes place at the terminal C=C bond in contrast to the above-mentioned palladium-catalyzed silaboration. The alkenyl iodide can be replaced with iodine or trimethylsilyl iodide. The key reaction intermediate seems to be silylpalladium(n) iodide, which promotes the insertion of allenes with Si-C bond formation at the central -carbon. 

Palladium-catalyzed oxidative allylic C-H functionalization provides attractive methods for the transformations of olefins, and their utility can be further enhanced by the development of more effective ways to use molecular oxygen (or air) to promote the catalytic cycle. The results outlined in this chapter summarize significant progress in the coupling reaction between terminal alkene and various types of nucleophiles. Further studies will be directed to explorations of the scope of nucleophilic reagents and olefins, and elucidation of the mechanisms of those reactions. Such studies will play an important role in the ongoing development of Pd-catalyzed C-H bond activations. 

On the other hand, Suzuki and co-workers have demonstrated that copper(I) species can promote the reaction of vinyl halides with terminal alkynes without the need for a palladium catalyst however, as in the Castro reaction, a stoichiometric amount of copper salt is needed. By contrast, Miura and coworkers found that aryl and vinyl iodides smoothly react with terminal alkynes in the presence of a catalytic amount of copper iodide using potassium carbonate as base when an appropriate amount of triphenylphosphine is added. Pyridine or 1,2-bis(diphenylphosphino)ethane (dppe) have been used as ligands in the case of Cul-catalyzed reaction of terminal alkynes with nitrones. ... 

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