Synthesis of 5-Substituted Tetrazoles: Reaction of Azide Salts with Organonitriles Catalyzed by Trialkylammonium Salts in Non-polar Media

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

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.

Tetrazoles: A multi-potent motif in drug design

The unique physicochemical properties and fascinating bioisosterism of tetrazole scaffolds have received significant attention in medicinal chemistry. We report recent efforts using tetrazoles in drug design strategies in this context. Despite the increasing prevalence of tetrazoles in FDA-approved drugs for various conditions such as cancer, bacterial viral and fungal infections, asthma, hypertension, Alzheimer's disease, malaria, and tuberculosis, our understanding of their structure-activity relationships, multifunctional mechanisms, binding modes, and biochemical properties remains limited. We explore the potential of tetrazole bioisosteres in optimising lead molecules for innovative therapies, discussing applications, trends, advantages, limitations, and challenges. Additionally, we assess future research directions to drive further progress in this field.

Al(OTf)3-Catalyzed Regioselective N2-Arylation of Tetrazoles with Diazo Compounds

Regioselective methods to access alkylated tetrazoles still remain a challenging goal. Herein, we describe a novel regioselective protocol for N2-arylation of tetrazoles with diazo compounds using inexpensive Al(OTf)3. This reaction could be conducted under mild conditions to access a diverse array of alkylated tetrazoles with 2-substituted tetrazoles as the major products, demonstrating a comprehensive range of substrate compatibility and excellent functional group compatibility. Mechanistic studies revealed a carbene-free process in this reaction procedure. Furthermore, the scale-up reaction and transformations of the N2-arylation of tetrazole products demonstrated the potential of this strategy.

Catalytic Tetrazole Synthesis via [3+2] Cycloaddition of NaN3 to Organonitriles Promoted by Co(II)-complex: Isolation and Characterization of a Co(II)-diazido Intermediate

The [3+2] cycloaddition of sodium azide to nitriles to give 5-substituted 1H-tetrazoles is efficiently catalyzed by a Cobalt(II) complex (1) with a tetradentate ligand N,N-bis(pyridin-2-ylmethyl)quinolin-8-amine. Detailed mechanistic investigation shows the intermediacy of the cobalt(II) diazido complex (2), which has been isolated and structurally characterized. Complex 2 also shows good catalytic activity for the synthesis of 5-substituted 1H-tetrazoles. These are the first examples of cobalt complexes used for the [3+2] cycloaddition reaction for the synthesis of 1H-tetrazoles under homogeneous conditions.

FSO2N3-Enabled Synthesis of Tetrazoles from Amidines and Guanidines

Herein we report the facile syntheses of tetrazoles enabled by FSO2N3 under mild conditions. FSO2N3 has been shown as the most powerful diazotizing reagent, which converts thousands of primary amines to azides fast and orthogonally. As the follow-up studies of the diazo transfer reaction using FSO2N3, we discover that amidines and guanidines are rapidly transformed into tetrazole derivatives when reacting with FSO2N3 under an aqueous environment, which is unprecedented for tetrazole synthesis.