Thiirans, Thietans, and Thiophen Derivatives

Thiirans, Thietans, and Thiophen Derivatives.— These classes of compounds have been grouped together since very few papers have appeared describing useful synthetic procedures. Apart from exchange reactions from oxirans, thiirans tend to be formed by roundabout routes. The dioxides (204) for instance may be prepared from diazoalkanes by reaction with sulphur dioxide. The reaction produces isomers accompanied by the dihydrothiadiazole dioxides (205). The formation of the thiiran, however, is favoured in polar solvents. 

A method of thietan (207) formation that promises to be widely applicable concerns the reaction of chalcones, which are available with a tremendous variety of substituents, and diethyl hydrogen phosphodithioate. A possible drawback is that cis/trans mixtures are obtained. There are very few examples of additions to non-activated alkynes an intramolecular example has now been shown to lead to thietan oxides (208) as well as larger sulphur heterocycles. 

5-Dihydrothiophens are readily available by Birch reduction of thiophens, and they may be alkylated adjacent to activating substituents. Subsequent removal of sulphur provides a useful route to substituted butadienes. Finally in this Section the preparation of l,2-dithiolo[3,4- f]pyrimidine-3-thiones merits a mention. The reaction of 6-arylaminouracils with carbon disulphide in the presence of sodium hydroxide and dimethyl sulphate gives good yields of the expected pyrimido[4,5-6]quinolines (210). However, upon acid work-up in the absence of Me2S04 the reaction follows a different course. The amino-function is lost and the sulphur heterocycles (209) are obtained. 

Kosugi, A. V. Anisimov, H. Yamamoto, R. Yamashiro, K. Shirai, and T. Kumamoto, Chem. Lett., 1981, 1341. 

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