The Aminopalladation-Reductive Elimination Tandem Reaction in the Construction of the Functionalized Indole Ring

The aminopalladation-reductive elimination tandem reaction of internal and terminal alkynes containing proximate nitrogen nucleophiles has been proved to be a powerful and useful tool for the construction of the substituted pyrrole nucleus of the indole system. The fact that the reaction can be carried out with a wide assortment of organopalladium precursors and readily available starting alkynes, the ease of execution and the tolerance of a wide range of functional groups highlights its importance and flexibility and may contribute toward its utilization in the synthesis of complex indole derivatives. The method may provide a versatile complement of well established classical methods such as the Batcho-Limgruber synthesis of indoles from o-nitrotoluenes and dimethylformamide acetals, the Fisher indole synthesis, the Gassman synthesis of indoles from N-halo anilines, the Madelung cyclization of N-acyl-o-toluidines, and the reductive cyclization of o-nitrobenzyl ketones.