Abstract Substitution by H 2 O in the presence of HCl and by NH (CH 3) 2 occurs at position 2 of 5-acetyl-2-benzylthio-6H-1, 3-thiazine without ring opening (in the first step for the amine). Substitution by the softer anion derived from diethylmalonate (and most likely HS−) occurs at position 6 with ring-opening. Subsequent cyclisations give the corresponding thiocarbonyl compounds. All these reactions are accompanied by elimination of the labile ...