Iron Salts in the Catalyzed Synthesis of 5-Substituted 1H-Tetrazoles

摘要

Tetrazoles are important heterocycles for explosives, photographic agents, and pharmaceuticals.[1] In the latter application, they can serve as metabolically stable surrogates of carboxylic acid groups.[2] Reactions between nitriles and azides lead to 5-substituted 1H-tetrazoles, and many synthetic approaches towards them have been developed.[3] For example, Sharpless and co-workers demonstrated that 1Htetrazoles could be accessed through the addition of sodium azide to nitriles in the presence of 0.5 to 1.0 equivalents of ZnII salts.[4] Later, Pizzo and co-workers showed that the metal salt could be replaced by tetrabutylammonium fluoride (TBAF; 0.5 equiv).[5] More recently, Yamamoto and coworkers catalyzed cycloadditions between nitriles and trimethylsilyl azide (TMS-N3) with 2.5 mol% of Cu2O, by performing the reaction in a 9:1 mixture of DMF and MeOH at 80 8C.[6] Copper proved to be a very efficient metal for this transformation. A one-pot multicomponent reaction was achieved by Kundu and co-workers, who applied a copper/ iron combination as catalyst in water for the formation of triazoles.[7] In this case, iron was suggested to serve as modulator for the oxidation state of copper. All of these approaches reveal that the catalytic formation of tetrazoles is still challenging and that the area demands to be developed further.