Abstract

Background: Oxadiazoles are privileged scaffolds in different areas of medicinal, pesticidal, polymer and material science. They act as anticancer, benzodiazepine receptor agonists, antimicrobial, analgesic, diuretic and tyrosinase inhibitors etc. A number of compounds containing an oxadiazole moiety are in late stage clinical trials including zibotentan and furamizole. Despite numerous methods are reported, the majority of them suffer from major drawbacks such as the use of strong alkaline or acidic conditions, highly toxic and corrosive reagents and also involve the use of costly reagents, elevated temperatures and longer reaction times. Inspired by the potential application of hypervalent iodonium reagents in organic synthesis, we would like to explore the readily available IBX and KI reagents for the facile synthesis of 1,3,4-oxadiazoles.

Method: Oxidative cyclization has successfully been developed for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles.

Results: An efficient process for the one-pot synthesis of 2,5-disubstituted 1,3,4-oxadiazoles has been developed using IBX/KI system at 25°C. The reaction was successful with a wide range of substrates such as aromatic and heterocyclic aldehyde and arylhydrazides to afford the corresponding unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles. The mild reaction conditions, cost-effective reagents and short reaction time are noteworthy advantages of this methodology.

Conclusion: We have developed a one-pot strategy for the synthesis of 1,3,4-oxadiazioles using a combination of IBX/KI at ambient temperature. This one-pot procedure proved to be quite general and worked well with a wide variety of aryl and heterocyclic aldehydes and variety of acylhydrazides. The advantage of this method lies in the simplicity of experimental procedure and the ready accessibility of the reagents, which render this, an experimentally attractive method for the preparation of unsymmetrical 1,3,4-oxadiazoles.

Keywords: Arylhydrazides, aldehydes, anticancer, corrosive reagents, 1, 3, 4-oxadiazoles, oxidative cyclization.

Graphical Abstract