Chemistry of acetylenic ethers XXXVI. Preparation and properties of some 1‐alkylthio‐1‐alkynes

Aldehydes can be converted into 1‐alkylthio‐1‐alkenes II (thioenol ethers) via either α‐chlorothioethers I by elimination of hydrogen chloride or, better, thioacetals VI by acid catalysed elimination of thiol. Bromination of the thioenol ethers II followed by subsequent dehydrobromination with diethylaniline and potassium hydroxide affords 1‐alkylthio‐1‐alkynes V, which are relatively stable liquids. Electrophilic as well as nucleophilic additions to 1‐ethylthio‐1‐propyne proceed slowly. The orientations during these additions are similar to those observed earlier for alkylthioethynes HCCSR; that is to say, that electrophilic as well as nucleophilic reagents attack the β carbon atom. This again39 suggests that the direction of the polarisability of the alkylthio group depends on the character of the substance added. During the approach of electrophilic reagents the polarisation is magnified image , but nucleophilic reagents induce the reversed polarisation magnified image .