1.2.3- Thiadiazoles. chemistry

The development of 1,3,4-thiadiazole chemistry is linked to the discovery of phenylhydrazine by Emil Fischer and of hydrazine by Th. Curtins in the late nineteenth century. The first 1,3,4-thiadiazole was described by Fischer in 1882, but the true nature of the ring system was demonstrated first in 1890 by Freund and Kuh. From 1894 Busch and his school took up work in this field, and they came to play a leading part in the rapid expansion during the first decades of the twentieth century. After a period of relatively low activity between the wars, interest was renewed due to the discovery of sulfa drugs... 

Another interesting application of thiadiazole chemistry is the synthesis of thiacrown ether. To this end, the precursor thiadiazole is treated with K2CO3 in the presence of 1,11-dichloro-3,6,9-trioxaundecane to give l,ll-bis(5-hydroxybenzofuran-2-sulfanyl)-3,6,9-trioxaundecane, which can be transformed into thiacrown ether 110 by treatment with tetraethylene glycol bis-tosylate and bases <00T3933>. 

Some typical rearrangements in this series have been reviewed in a different context, concerning 1,2,4-thiadiazole chemistry [82AHC(32)285]. 5-Amidinothiadiazoles 240, obtainable from the 5-amino-3-methyl-l, 2,4-... 

The period from 1889 until the early 1960s of 1,2,5-thiadiazole chemistry has been reviewed at key intervals . The two decades (1960-1980) which show a virtual explosion in the area have been comprehensively reviewed <84CHEC-I(6)5I3>. In this chapter, the literature from 1981 to 1994 is surveyed with emphasis on novel findings, useful extensions, and confirmation of previous hypotheses. 

The majority of 1,2,3-thiadiazole chemistry has been directed toward the study of thermal and photochemical reactions. Upon thermolysis 1,2,3-thiadiazoles afford a number of varied products (77T449, 77JOC575) as illustrated in equation (1). The mechanism of formation of the myriad of products has received considerable attention. 

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