A new approach for the synthesis of α‐ketothioamides from methyl ketone, pyrrolidine/piperidine and elemental sulfur using recyclable magnetic catalyst

Abstract

Backgroundα‐ketothioamides play a vital role in the fields of medicine and biology. There are many α‐ketothioamide synthesis pathways, but in general, most current methods are either conventional heating in solvent conditions or using non‐recyclable catalysts. Thus, our work investigated the preparation of α‐ketothioamides under solvent‐free sonication using magnetic nanoparticle immobilized chlorozincate ionic liquid as a catalyst. The desired products were purified by chromatography columns and characterized by 1H NMR and 13C NMR.ResultsIn this study, Lewis acidic ionic liquid grafted onto a magnetic nanoparticle (Fe3O4@IL‐ZnCl2) was used as an effective heterogeneous catalyst for the generation of a variety of α‐ketothioamide derivatives. The optimized conditions were methyl ketone (1.0 mmol), amine (1.2 mmol), S8 (1.2 mmol), and Fe3O4@IL‐ZnCl2 (15 mg) under solvent‐free sonication at 80 °C for 5 h, and the crude products were obtained in a 34–94% isolated yield. Then, this procedure was successfully applied to a wide range of aryl and alkyl ketone compounds. Besides, there was a little loss in catalytic activity in three consecutive cycles, indicating the reusability and stability of the catalytic system.ConclusionsWe have successfully designed a novel protocol for the generation of α‐ketothioamide derivatives from aryl/alkyl methyl ketones, amines, and elemental sulfur catalyzed by chlorozincate ionic liquid‐coated magnetic Fe3O4 nanoparticles. The reaction proceeded at a mild, efficient solvent‐free sonication accompanied by a well‐reactive catalyst, which is easily separated and reusable. Besides, a feasible mechanism was presented.This article is protected by copyright. All rights reserved.

Synthesis of α-ketothioamides with elemental sulfur under solvent-free conditions in a mixer mill

“…An advanced version of this method is solvent-free, but relies on sonication at 80 °C for 5 h and the use of an ionic liquid (IL)-modified iron nanoparticle catalyst (Fe 3 O 4 @IL-ZnCl 2 ), which is time-consuming to prepare following a multistep procedure. 9 In the second approach towards α-ketothioamides (b), sulfoxonium ylides are used as starting material. 10 The method is of interest because it neither needs a metal catalyst, nor a base or additive.…”