Ruthenium-Catalyzed Oxidative Annulation of 6-Anilinopurines with Alkynes via CH Activation: Synthesis of Indole-Substituted Purines/Purine Nucleosides

Indole‐substituted purine nucleobases have been synthesized by Ru‐catalyzed oxidative annulation of 6‐anilinopurines with internal alkynes that involves CH activation. Unsymmetrical aryl(alkyl)alkynes led to high regioselectivity. The reaction was also successful with nucleosides by delivering unprotected indole‐substituted nucleosides. In the presence of [RuCl2(p‐cymene)]2 and copper(II) acetate hydrate [Cu(OAc)2⋅H2O], in some cases, we have observed two‐fold CH activation products that exhibit fluorescence. A ruthenacycle intermediate was characterized by crystallography, which suggests that the N‐1 nitrogen atom of the purine acts as a directing group for the present transformation.