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Thermischer Zerfall isomerer Dihydro‐1,3,4‐thiadiazol‐1,1‐dioxide 1)
Author(s) -
Quast Helmut,
Kees Frieder
Publication year - 1981
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19811140238
Subject(s) - chemistry , thermal decomposition , sulfur dioxide , conrotatory and disrotatory , steric effects , azine , sulfur , decomposition , medicinal chemistry , photochemistry , electrocyclic reaction , photodissociation , organic chemistry , bicyclic molecule , ring (chemistry)
Thermal Decomposition of Isomeric Dihydro‐1,3,4‐thiadiazole 1,1‐Dioxides 1) After a review of both the thermolysis and the photolysis of 2,5‐dihydro‐1,3,4‐thiadiazoles 3 , containing sulfur of various levels of oxidation, the thermolysis of the isomeric di‐ tert ‐butyl‐dihydrothiadiazole 1,1‐dioxides cis ‐ 6 , trans ‐ 6 , and 17 is described. Loss of sulfur dioxide and formation of the azine 16 from cis ‐ 6 occur smoothly already at 50°C. In contrast, only above 145°C trans ‐ 6 as well as 17 split into the alkylidenehydrazide 18 and sulfur monoxide which disproportionates into sulfur and sulfur dioxide. A concerted [4 + 1]cycloelimination of sulfur dioxide from trans ‐ 6 is avoided because of unfavourable steric interactions. Since on the linear cheletropic path, decomposition had to proceed in the disrotatory way the result would be the sterically impossible ( E , Z , s ‐ cis )‐conformation of the azine 16 .