Thiazolines 1.3.4- thiadiazines

The amidine 61 when treated with alkylsulfonyl chlorides forms the intermediate thiazoline diazadiene 62 which cyclises to give the thiazolo[3,2-6]-l,2,4-thiadiazine-l,1-dioxide 63 in moderate yield. This is the first synthesis of this class of compound <02TL4099>... 

Whether a 3-amino-J4-thiazohne-2-thione (CCXVII) or a 3,4-dihydro-2H-1,3,4-thiadiazine-2-thione (CCXVIII) is obtained depends in fact on the reaction conditions. Sandstrom (301, 302, 303) found, furthermore that the thiadiazines (CCXVIII) are readily converted to the thiazolines (CCXVII) by refluxing the former with alcoholic hydrogen chloride. 

Sato and Ohta (307) who reinvestigated the reaction of dithiocarbazic acids with chloroacetone and w-bromoacetophenone also described the 3.4-dihydro-2H-1,2,4-thiadiazine-2-thione structure to the products. These authors also describe the condensation of N-benzoyl dithiocarbazic acids (CCXV, Rj—CgHjCO with a-halo ketones which yields 4-benzoyl-3,4-dihydro-2H-t, 3,4-thiadiazine-2-thiones (CCXVIII, These products hydrolj ze in acid medium (with formation of benzoic acid) and simultaneously undergo a transformation to 3-amino-zl4-thiazoline-2-thiones. These facts support the remarks made earlier. 

The 3-amino-J4-thiazoline-2-thiones are listed in Table 34, the isomeric 3,6-dihydro-2H-l,3,4-thiadiazine-2-thiones in Table 36 and the... 

Alkylthiazolines undergo cyclization reaction with chlorosulfonyl isocyanate in the presence of triethylamine to give thiadiazines and thiazolidine fused thiadiazines <93SC121>. In the case of the reaction between 2-phenyl-2-thiazolines the two products (84) and (85) shown in Scheme 15 are formed. The latter should arise from the former by the action of water. 

Little chemistry has been carried out on the thiadiazine systems, which are much less stable than their oxygen analogues, and readily undergo ring contraction to pyrazoles and/or thiazolines under a variety of reaction conditions (Sections 6.17.5.1 and 6.17.5.2). There are no reports on the preparation of 12 ,3,4-thiadiazines and only isolated examples of 1,3,4-thiadiazine 5,5-dioxides have been synthesized. Also unknown are examples of the fully conjugated 1,3,4-oxonia- and 1,3,4-thionia-systems (7 X = O and S, respectively). 

The synthesis of 2-amino-6//-l,3,4-thiadiazines (276) by condensation of a-haloketones (274) with thiosemicarbazides, as first reported by Bose <25JIC51,25JIC95) continues to be used as a reliable route to this system. The reaction, however, can be complex and the products are dependent on the nature of the substituents in each of the reactants, the polarity of the solvent used, and the reaction temperature <91CHE666> common by-products are 2-hydrazinothiazoles (275) and 3-amino-thiazolines (see Section 6.17.5.2). An excellent review of the confusing and sometimes erroneous pioneering work on these reactions is available . 

Two excellent papers on YE aroma have arisen recently from Werkhoff s group at Haarmann and Reimer in Germany (13,14). Fifty sulfur compounds were reported in the first study (13) while 115 such components were described in the second paper (14). Aliphatic compounds, sulfur-substituted furans, thiophenes, thiazoles, 3-thiazolines, cyclic polysulfides, perhydro-l,3,5-dithiazines, a perhydro-1,3,5-oxathiazine, a perhydro-l,3,5-thiadiazine and aliphatic and heterocyclic dithiohemiacetals were all mentioned, and the structures of most of the newly identified compounds were confirmed by synthesis. These sulfur compounds elicit a wide variety of aromas but are often savory, e.g., meaty, vegetable-like, and YEs are a valuable source of potent components which provide meaty notes. 

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