4H-l,3,4-Thiadiazin-5-ones

Still in connection with the formation of isomers in these cyclization reactions, it is noteworthy that S-alkyl dithiocarbazates react with chloroacetic acid (302) and co-bromoacetophenone 84) to give 2-alkyl-thio-5,6-dihydro-4H-l, 3,4-thiadiazin-5-ones and 2-alkylthio-5-phenyl-4H-1,3,4-thiadiazines respectively. 

Dihydro-4H-l,3,4>thiadiazin-5-ones from 1,3,4-thiadiazolium salts and acylphosphonic acid esters... 

When the dihydro-1,2,4-triazinone 76 is heated at 180°C with red phosphorus and hydroiodic acid, there is rupture of the 1,2-bond and subsequent ring closure to give 4,5-diphenylimidazolin-2-one (77) (see Scheme 17) and reductive ring contractions to imidazoles (81) have also been reported " in the 1,3,5-triazine series. A further interesting ring contraction is that which occurs when 4H-l,3,5-thiadiazines (78) are treated with aliphatic amines at room temperature. The triarylimidazoles (81) may be formed by initial formation of the 1,3,5-thiadiazine anion (79) which probably loses sulfur... 

Equimolar amounts of N,N-dimethylcarbamylisothiocyanate and benzylidene-methylamine in ether allowed to stand 1 hr. at room temp, in a closed flask 2-dimethylamino-5-methyl -6-phenyl -5,6-dihydro-4H-l, 3,5- thiadiazin-4-one. Y 82%. F. e., prepn. of carbamyltbiocyanates, RgNCO-S-C = N, and related reactions, s. J. Goerdeler and D. Wobig, A. 757, 120 (1970). 

Tetrachloro-4H-l,2,6-thiadiazine added dropwise at 10° under to excess formic acid with stirring, which is continued overnight -> 3,5-dichloro-4H-l,2,6 thiadiazin-4-one. Y 85%. J. Geevers and W. P. Trompen, R. 93, 270 (1974). 

A soln. of triphenylphosphine in abs. ether added gradually at 0° under Ng well-stirred soln. of 5-ferf-butyl-l,2,4-dithiazol-3-one in the same solvent, the resulting triphenylphosphine sulfide removed by filtration in the cold, and the soln. of the thioacylisocyanate obtained treated with N-benzylideneisopropylamine in abs. ether 6-fert-butyl-3-isopropyl-2-phenyl-2,3-dihydro-4H-l,3,5-thiadiazin-4-one. Y 91%. F. e. s. J. Goerdeler and K. Nandi, B. 108, 3066 (1975). 

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