Thioamides are great importance in medicinal chemistry due to their biological activity. For example, against bacterial infection, anti-fungicides, herbicides and anti-ulcerative agents. Thioamide intermediates are versatile in synthesis of pharmaceutical ingredients, such as Diclofenac, Fenclofenac, Ibufenac, Naproxene and in peptide chemistry. Furthermore, the thioamide derivatives can be readily converted to the corresponding carboxylic acids or thioesters. Therefore, developing of more efficient methods working under mild condition is in high demand. Thioamides are traditionally prepared by thionation of the corresponding amides using phosphorus pentasulfide or the Lawesson reagent. Surprisingly, the Willgerodt–Kindler reaction for thioamide synthesis has received very little attention (especially in recent years). Today, the Willgerodt–Kindler reaction can be classified as a one-pot, three-component process for the synthesis of synthetically useful (thio) amides.
In continuation of our interest to use biopolymers for organic transformations, Cu(I)@Chitosan was used as an efficient heterogeneous nano-bio catalyst for Willgerodt–Kindler reaction. This catalyst can be played a considerable role in thioamide bond formation. Easy preparation and separation, mild acidity and basicity, stability and reusability of the catalyst, motivated us to explore its potential to catalyze reaction. Using ultrasound irradiation as a clean source of energy, aqueous media, ambient temperature, high yield and short reaction time are outstanding features of this work.
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