Stereospecific synthesis of cis- and trans-2-halogenovinyl ketones. Stereochemistry of nucleophilic substitutions at vinylic carbon

Hydrogen and deuterium halides combine with ethynyl ketones at –40° to give predominantly cis-2-halogenovinyl ketones, and at 20° to give trans-2-halogenovinyl ketones exclusively. The halides can be converted into 2-phenylthiovinyl ketones and into 2-phenylsulphonyl ketones with retention of configuration. The trans-halogenovinyl ketones and the trans-sulphones are thermodynamically more stable than the respective cis-isomers; however, the trans-sulphides are less stable than the cis-sulphides. The behaviour of the sulphides is interpreted in terms of electrostatic interaction between the sulphur atom and the carbonyl oxygen.