Polystyrene-bound AlCl3 – a catalyst for the solvent-free synthesis of aryl-substituted tetrazoles†

Abstract

Tetrazole moieties are components of various pharmacologically active molecules. Several synthetic protocols for the synthesis of tetrazoles have been developed. Among those, the reaction of organic nitriles with azides catalyzed by Lewis acids (LAs) provides a convenient access. Nevertheless, generally rather harsh reaction conditions have to be utilized for such syntheses. We have developed a simple, solvent-free procedure which allows a convenient isolation of tetrazoles using a heterogeneous catalyst: we show that polystyrene/AlCl₃ composites produce tetrazoles at reasonable yields and allow a simple work-up procedure. We have characterized the AlCl₃/polystyrene composite (gas sorption, XRD, IR) and investigated its efficacy in the preparation of aryl-substituted tetrazoles. We also have evaluated MgCl₂, CuCl₂, and ZnCl₂ as Lewis-acid catalysts, but they are clearly outperformed by AlCl₃ correlating with the Lewis-acid strength on the Gutmann-Beckett scale.