Modular, Step-Efficient Palladium-Catalyzed Cross-Coupling Strategy To Access C6-Heteroaryl 2-Aminopurine Ribonucleosides

Two Pd-catalyzed methods to access 6-haero- aryl 2-aminopurine ribonucleosides from 6-chloroguanosine are described. First,Pd-132-catalyzed Suzuki-Miyaura cross-Coupling, using a series of boron substrates and 6-Chlorogua-nosine forms 6-heteroaryl-2-arninopurines in a single step. The versatility of 6-chloroguanosine is further demonstrated using a modified Sonogashira coupling employing potassium iodide as an additive. Finally, the utility ot the 6-alkynyl-2-aminopurine ribonucleoside as a dipolarophile in [3 + 2] cycloadditions is presented, affording triazoles and isoxazoles when reacted with azide and isonitrile.1,3-dipoles, respectively.