Argon-Matrix Isolation of Bis(carbomethoxy)thiirene: Formation of Acyl and Carbalkoxythioketenes

Thiirene, Thioketene, 1,2,3-Thiadiazole, Thio-Wolff Rearrangement Photolysis of argon-matrix isolated 4,5-bis(carbomethoxy)-l,2,3-thiadiazole with A = 254 or 265 nm resulted in the almost quantitative formation of bis(carbomethoxy)thiirene (3g). Photolysis of 3g could only be carried out by long irradiation times at short wavelength A = 210nm and resulted mainly in extensive fragmentation instead of the formation of bis(carbomethoxy)thioketene, confirming earlier predictions that substituents, especially electron-withdrawing ones, should stabilize the thiirene ring. Methylcarboethoxy and methylacetylthioketene were obtained, however, in the argon-matrix photolysis or flow thermolysis of 4-methyl-5-carboethoxyor 4-carboethoxy-5-methyl-l,2,3-thiadiazole and 4-acetyl-5-methyl-l,2,3-thiadiazole, respectively.