Oxathiolan-5-ones

Heating cyclic mono-, di- or tri-thiocarbonates, usually in the presence of base, gives thiiranes and carbon dioxide, carbon oxysulfide or carbon disulfide respectively. The methiodide salts of 2-methylimino-l,3-oxathiolanes are converted to thiiranes with high stereoselectivity, except for 5-aryl-substituted oxathiolanes (Scheme 146) (80LA1779). Flash vacuum thermolysis of l,3-oxathiolan-5-ones causes loss of carbon dioxide and nearly quantitative formation of thiiranes of inverted configuration (Scheme 147) (80JA744). For example, thermolysis of c/s-2,4-diphenyl-1,3-oxathiolan-5-one gives trans-2,4-diphenyl-thiirane. 

Two types of sulfur-containing five-membered heterocycles are convenient precursors of thiocarbonyl ylides, namely, 2,5-dihydro-1,3,4-thiadiazoles (20) and 1,3-oxathiolan-5-ones (21) (Scheme 5.5). The precursors 20 are accessible by two different methods. 

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