Stereoselective synthesis of 4H-5,6-dihydro-1,3-thiazines by the reaction of 3-N-acylamino alcohols with Lawesson's reagent

The 4H-5,6-Dihydro-1,3-thiazine derivatives 13-15 were obtained exclusively and stereoselectively in fair yields by treating the 3-N-acylamino alcohol s 5-8 with an equimolar amount of Lawesson's reagent (LR), while the corres ponding thiols 9-12 were afforded stereoselectively when only 0.5 equiv. of LR was used in this reaction.