Synthesis of new 2H-1,4-thiazines and their derivatives utilizing N,N-(di-n-alkyl)-N′-arylthiocarbamoylamidines

The reactions of N,N-(di-n-alkyl)-N'-arylthiocarbamoylamidines (1) with 2-bromo-1-phenylethanone in the presence of K2CO3 in THF at reflux gave 3-(di-n-alkylamino)-2-arylimino-5-phenyl -2H-1,4-thiazines (7) in 32 to 62 % yields. Treatment of compounds 1 with bromoacetyl bromide in the presence of pyridine in CH2Cl2 at 0 degrees C afforded 5-(di-n-alkylamino)-6-arylimino-2H-1,4-thiazin-3- ones (12) in 41 to 84 % yields, whereas the same reactions of 1 with 2-bromopropionyl bromide under the same conditions gave 4-(di-n-alkylamino)-5-arylimino-2-(1-bromoethylidene)-2H-thiazolines (17) as minor compounds in addition to thiazin-3-ones 16, analogous to compounds 12. The reactions of 1 with ethyl bromoacetate in CH2Cl2 at room temperature, however, gave [(arylimino)(S-ethoxycarbonylmethyl)]methyl-N,N-(di-n-propyl) amide hydrobromides (19) in 71 to 88 % yields. Compounds 7, 12, 16, 17, and 19 are all new and the mechanisms of their formations are proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.