The synthesis and structure elucidation of the four diastereo-mers (e.g I and II) of (2R)-1-ethylsulfinyl-1-ethylthio-2,3-dihydroxypropane 2, 3, 4 and 5, and their acetyl derivatives together with the trityl derivatives 2 and 5 are reported. The crystal and molecular structures of 2 and 5 were determined by X-ray crystallographic techniques. These compounds crystallize in the space groups P2₁ and P2₁2₁2₁, respectively, with a=9.851(2), b=12.547(3), c=9.947(2) A, b=116.99(2) Z=4, and a=13960(3), b=13.640(3), c=5.673(2) A, Z=4, respectively. The synthesis of ketene dithioacetal monoxides with 100% enantiomeric purity at the sulphur atom of the sulfoxide group is also reported.