Oxathietanes

Another study16 investigates the effect of benzene ring fusion on the reactivity of 1,2-Oxathietane. Ab initio calculations were performed using the 3-21G and the 6-31G basis sets, at Hartree-Fock and MP2 calculational levels. It was found that the allowed (8s + 2s) cycloreversion is unfavorable energetically. A subsequent experimental and theoretical study17 favors biradical intermediates in the valence tautomerism of benzoxathiete to monothio-o-benzoquinone. 

Flash vacuum thermolysis of 1,2,3-oxadithiolane 2-oxide has been reported to proceed via the intermediacy of 1,2-oxathietan <82JCS(P2)279>. The gas-phase thermolysis of 1,2,3-benzoxadithiole 2-oxide (37) proceeds in an analogous manner to the thermolysis of 1,3,2-benzodioxathiolane 2-oxide (49), affording cyclopentadienethione <81AG(E)570>. 

The present review is concerned with four-membered heterocycles that contain one sulfur atom either alone or associated with another heteroatom. The classes of compounds that will be discussed are the thietanes (1) and thietes (2), the 1,2-oxathietanes (3), the / -sultines and -sultones (4 and 5), the 1,2- and 1,3-thiazetidines (6 and 7) and thiazetes (8), the 1,2- and 1,3-thia-phosphetanes (9 and 10), and the 1,3-silathietanes and 1,3-selenathietanes (11 and 12). 

Preparation of stable -sultines. Crystal structure of 2,2-bis(p-fluo-rophenyl)-3,3-dimethyl-1,2-oxathietan 2-oxide. ... 

The most surprising aspect is the number of rings that are planar or nearly so. The notable exceptions are the 1,2-diazetidine, the 1,2-dioxetane and the 1,2-oxathietane oxide rings. However, the reason for lack of planarity is not clear. 

The IR of 1,2-oxathietane dioxide shows an asymmetric S02 stretch at 1394 and a symmetric one at 1176 cm 1 (67DOK(172)1327). The corresponding monoxides appear at 1150 cm"1 (75CC724). The chemical shifts and coupling constants have been used to assign the cis and trans structures to 3,4-dimethyl-1,2-oxathietane dioxide (73CC841). 

The thermal decomposition of 1,2-oxathietane 2-oxides invariably leads to loss of sulfur dioxide and accompanying alkene formation (Scheme 17) (73JA3420, 78BAU142). The lack of any solvent polarity effect on rate (75CC724) as well as supporting theoretical calculations favor a concerted loss of sulfur dioxide without requiring a strained [[Pg.459]

The intermediacy of a 4-imino- 1,2-oxathietane 2-oxide from the addition of sulfur dioxide to ketenimines was inferred from the trapping with methanol. The final isolated product in absence of methanol, l,2-thiazetidin-3-one 1-oxide, was established by X-ray (Scheme 42) (81CC350). 

Perfluorinated 1,2-oxathietane dioxides, /3-sultones, are the most stable derivatives and, as such, the most widely studied. They undergo some of the more unique reactions, especially those with acid halides which are regarded mechanistically as a concerted displacement (Scheme 53) (67BAU1935). 

The parent 1,2-oxathietane ring has not been made by formal [2 + 2] additions however, both S02 and S03 are known to add alkenes under certain conditions. 

Several examples of polyhalogenated alkene addition to sulfur dioxide (60JA6181, 66JCS(C)ll7i> are known to give moderately stable 1,2-oxathietane 2-oxide adducts (Scheme 99) (78BAU142, 79BAU106). 

Acid-catalyzed rearrangement of 1,1 -diphenyl-2,2-dimethylpropanol in presence of sulfur trioxide forms a stable 1,2-oxathietane 2,2-dioxide (Scheme 18) (77JCS(P1)247). 

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