Thioxocarbenes, Thiirenes, and Selenium Analogs

Early work on these species has been summarized. In the meanwhile, thiirene (99) and several substituted derivatives, as well as selen-irene, have been matrix-isolated and observed by IR spectroscopy on photolysis of 1,2,3-thiadiazoles or selenadiazoles (Eq. 27). The same species are also obtained by photolysis of vinylene trithiocarbonates (100).  

The photolysis of benzothiadiazole at 8 K gave a species which has not yet been fully identified but may have been benzothiirene (101). Further irradiation caused rearrangement to the thioketene 102 (Eq. 28).  

Previous evidence for the existence of benzothiirene in solution had been reported by Cadogan et who obtained a mixture (about 1 1) of thi-anthrenes 103 and 104 by thermolysis of sodium o-bromobenzenethiolate (Eq. 29). 

Using similar criteria, the involvement of benzothiirene in the thermolysis and photolysis of 1,2,3-benzothiadiazole was indicated by the isolation of mixed thianthrenes or thiophenols, although a report to the contrary has 

while definitive proof is still lacking, the existence of benzothiirene, like that of IH-benzazirine (Section III), is fairly certain. In contrast, all attempts to find evidence for benzoxirene as an intermediate in similar reactions have failed (thermolysis of sodium o-bromophenoxide, and flash pyrolysis of o-quinonediazide, salicylic acid or its methyl ester, including methyl [l- C]salicylate ). Calculations indicate, however, that the energy differences between oxirene and formylcarbene on the one hand, and thiirene and thioformylcarbene on the other, are fairly similar.  

Flash thermolysis is a convenient way of producing thioketenes from 1,2,3-thiadiazoles.134,138,139 Thiirenes are formed prior to thioketenes in the gas phase140 or matrix127 photolysis of 1,2,3-thiadiazoles. 

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