2-Aminoindoles and 2-Iminoindolines as Viable Precursors of Indole-Fused Nitrogenated Polyheterocycles

The synthesis of architecturally complex polyheterocyclic structures embedding the indole ring represents a growing field of interest. Carbolines and their partially dehydro derivatives, pyrazinoindoles, indoloindoles, azepinoindoles and other mediumsized derivatives are only some examples of indolecontaining polycyclic compounds featured by enhanced pharmacological and photophysical properties. Among various synthetic protocols to prepare these important target compounds those based on the utilization of 2-aminoindoles and 2-iminoindolines are gaining increasing interest because of the ease of their preparation. The presence of a couple of reactive sites in these derivatives is instrumental for the assembling of polyheterocyclic structures exploiting single step operations featured by efficient cascade or tandem processes. Several of these methods employ catalyzed reactions which can be developed for the asymmetric synthesis of enantiopure compounds. This review provides an up-to-date report on the currently available methods for the synthesis of 2- aminoindoles and 2-iminoindolines and their application to the preparation of polyheterocyclic derivatives.