Reactions of (ClSN)3 or FSN with 2-chloropentafluoro-1,3-butadiene provide the 1l4,2-thiazines I (R = Cl, F). Fluorination of I (R = Cl) with KF gives 88% I (R = F). MeOH reacts with I (R = F) to form I (R = OMe). The structure of I (R = OMe) was detd. by single-crystal X-ray diffraction anal. With water I (R = Cl) forms the 1,2-thiazin-3-one 1-oxide II.