1.2.5- Thiadiazole 5-oxide

Thiadiazoles undergo substitution reactions reflecting their relatively high aromatic character but in contrast the 1,2,5-thiadiazole 1-oxides and 1,1-dioxides suffer addition chemistry supporting their non- or antiaromatic characters. 

Ring Enlargement of Five-Membered Heterocycles (Aminolysis of 1,2,5-Thiadiazole 1-Oxides)... 

Physical Properties of 1,2,5-Thiadiazoles. An inversion barrier was theoretically and experimentally investigated for 1,2,5-thiadiazole 1-oxides (pyramidal, SO structure). The crystal and molecular structures of sulfametrole have been determined. ... 

Chemical Properties. - 3>4-Dimethyl-1,2,5-thiadiazole reacts with benzyne to give (346),(347), MeCN and Sg. Similar results were obtained for the Se analogue, but yields were very low (1-2 ) . Unsymmetrical diamines (348) can be formed from 3,4-dimethoxy-1,2,5-thiadiazole 1-oxide by reaction with ArNH2 then NH. ... 

Lumma, W.C., Jr., Anderson, P.S., Baldwin, J.J., Bolhofer, W.A., Habecker, C.N., etal. (1982) Inhibitors of gastric acid secretion 3,4-diamino-1,2,5-thiadiazole 1-oxides and 1,1-dioxides as urea equivalents in a series of histamine H2-receptor antagonists. J. Med. Chem. 25 207 -210. 

Similarly, cyclic sulfite and cyclic sulfate esters of the corresponding 1,2-diamines have been named 1,2,5-thiadiazole 1-oxide (5) and 1,2,5-thiadia-zole 1,1-dioxide (6). In this chapter, emphasis is placed on cyclic sulfites and cyclic sulfates however, the synthetic preparation and nucleophilic transformations of cyclic sulfamidites and cyclic sulfamidates are also compared. 

Thiadiazole oxides and reduced forms are readily prepared via [4 -h 1] cyclizations (Table 4). The reagents employed for this purpose are thionyl chloride, sulfuryl chloride, sulfur tetrafluoride, N,N -bis(p-toluenesulfonyl)sulfur diimide, cyclic diimides, pentafluoroethyliminosulfur difluoride and sulfamide. 

In a smdy undertaken on antagonists of the dihydropyridine neuropeptide Yi receptor, common bioisosteres such as thiourea and cyanoguanidine were examinated as urea replacement (Figure 15.37) and also more uncommon derivatives like squaric acid and thiadiazole oxide. 

Khosropour AR, Noei J (2010) A convenient strategy for the synthesis of 3,5-diaryl-l,2,4-thiadiazoles oxidative dimerization of arylthioamides using CC-DMSO in PEG-400. MonatshChem 141 649-651... 

Diaryl-l,2,3-thiadiazole 1,1,2-trioxides (24) are photolysed to nitriles (25), small amounts of diarylalkynes (26), and intermediates (27), which, in the presence of aqueous methanol, react further to yield hydroxamic acids (28). A mechanism has been proposed correlating these findings with the photolysis of other 1,2,3-thiadiazole oxides. ... 

C2N2S s N N — — 5-Acylamino-3-methyl-l,2,3-thiadiazole 5-phenyl-l,2,3-thiadiazole 3-oxide... 

In contrast to thiazoles, certain isothiazoles and benzisothiazoles have been directly oxidized to sulfoxides and sulfones. 4,5-Diphenyl-l,2,3-thiadiazole is converted by peracid into the trioxide (146). Although 1,2,5-thiadiazole 1,1-dioxides are known, they cannot be prepared in good yield by direct oxidation, which usually gives sulfate ion analogous to the results obtained with 1,2,4- and 1,3,4-thiadiazoles (68AHC 9)107). 

Azole 7V-oxide groups are readily removed by reduction with Zn/HOAc, HI or PCI3, e.g. in the pyrazole series. 1,2,3-Thiadiazole 3-oxides isomerize on irradiation to the corresponding 2-oxides. 

Thiirenes have been isolated in argon matrices at 8 K by photolysis of 1,2,3-thiadiazoles or vinylene trithiocarbonates (Scheme 151) (80PAC1623, 8UA486). They are highly reactive and decompose to thioketenes and alkynes (Scheme 22). Electron withdrawing substituents stabilize thiirenes somewhat, but no known thiirene is stable at room temperature unlike the relatively stable thiirene 1-oxides and thiirene 1,1-dioxides. 

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