The general procedure for the synthesis of 1-methylpyrrolidin-2-thione from N-methylpyrrolidone was as follows: N-methylpyrrolidone (0.75 mmol) was dissolved in tetrahydrofuran (THF, 5 mL) in a microwave reaction flask, followed by the addition of phosphorus pentasulfide/aluminum oxide (P2S5/Al2O3, 0.53 g, equivalent to 0.90 mmol of P2S5). After sealing the reaction vial, the suspension was placed in a CEM Discover microwave reactor and heated by microwave radiation at 60 °C and 60 W power with stirring and air cooling. After 5 min of reaction, the completion of the reaction was confirmed by thin layer chromatography (TLC) monitoring. The reaction solution was cooled and quickly filtered through a short silica gel column. The reaction was first eluted with hexane to remove non-polar impurities, followed by a solvent mixture of hexane/ethyl acetate (EtOAc) to recover the target product 1-methylpyrrolidine-2-thione. Finally, the solvent was removed by distillation under reduced pressure to afford pure 1-methylpyrrolidine-2-thione in 92% yield.
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