The first ionic liquid-promoted one-pot diastereoselective synthesis of 2,5-diamino-/2-amino-5-mercapto-1,3-thiazin-4-ones using masked amino/mercapto acids

The first expeditious synthesis of 2,5-diamino-/2-amino-5-mercapto-1,3-thiazin-4-ones from masked and activated amino/mercapto acids, viz. 2-phenyl-1,3-oxazol-5-one or 2-methyl-2-phenyl-1,3-oxathiolan-5-one, aromatic aldehydes and thioureas using the ionic liquid [Bmim]Br as an environmentally benign reaction promoter is reported. The synthesis is highly diastereoselective and involves tandem Knoevenagel, Michael and ring transformation reactions in a one-pot procedure. The sequential reaction pathway is supported by the isolation of arylidene derivatives and their Michael adducts with thiourea, and quantitative conversion of the latter into the final products under the same reaction conditions.