Thiirens and Thiiren Oxides

A review has appeared. The preparation and observation by a second research groups of thiirens from 1,2,3-thiadiazoles by irradiation at low temperature (8 K) (see Vol. 5, p. 197) has engendered a spirited discussion of its i.r. spectrum. . 46 initio calculations of the structure and the i.r. spectrum of thiiren lead to the conclusion that thiiren is properly anti-aromatic, but cast doubt on the existence of a disputed band at 660 cm . Thiirens have also been prepared by irradiation of vinylene trithiocarbonates at low temperatures and of 1,2,3-thiadiazoles in the gas phase. Both 4- and 5-methyl-1,2,3-thiadiazoles give (60) in the presence of hexafluorobut-2-yne. Similarly, (61) and (62) give the same ratio of isomeric 2- or 3-methyltriphenylthiophens upon thermolysis in the presence of diphenyl-acetylene.  

A C-labelling experiment has established firmly that (63) does not give (64). Chemical labelling of benzothiadiazole (65) has established that, in the presence of 

A full paper detailing the preparation and chemical properties of diphenylthiiren 1-oxide has appeared.The reactions of thiiren 1,1-dioxides with a-metallated isocyanides and lithium azide have been reported. The latter leads to a new heterocyclic system (69). Dimethyl- and diphenyl-thiiren 1,1-dioxides are reported to react with the 1,3-dipoles (70) and (71) to give (72) or (73) respectively. In the case of (71) and diphenylthiiren 1,1-dioxide, (74) is also formed. The Diels-Alder reaction with a diene-amine, but not the structure of the product, is mentioned in the same report. 

Some of the recent papers on thiirenium ions are listed in the bibliography on page 232. 

5 Three-membered Rings with More than One Heteroatom 

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