Potassium methylxanthate

Ring opening of 5,6-dideoxy-5,6-epithio-l,2-0-isopropylidene-/3-L-idofiiranose with potassium methylxanthate leads to 1,2-O-isopropyl-idene-5,6-dithio-5,6-S-thiocarbonyl-/3-L-idofuranose, which can be reductively cleaved with lithium aluminum hydride to 1,2-O-isopro-pylidene-5,6-dithio-)3-L-idofuranose. Acid hydrolysis of the latter compound would be expected to give a 1,6-anhydroidose derivative having a sulfur atom in both the pyranose ring and the anhydro ring, but a definitive product was not isolable. 

The episulfides (82), (83), (84), and (87) react readily with potassium methylxanthate in methanol at room temperature to give crystalline tri-thiocarbonate derivatives. Assuming attack at the primary position,the reaction from (84) may be formulated as follows. 

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