An Unusual C-1C-2 Ring-Splitting of Pyranosides by a Retro-Aldol Reaction - a Route to New Chiral Building Blocks

The treatment of the α‐oxoketene dithioacetal sugar derivatives 2 and 7 with concentrated hydrochloric acid in THF leads to the open‐chain uloses 3 and 8. The reaction mechanism can be rationalized as a retro‐aldol reaction. This rationalization was supported by reacting 2 and 7 with DCl/D2O. Compound 3 was converted into the chiral pyrazoles 12 and 13. The branched‐chain ulose 2 forms the thiopyranosidulose 15 when treated with diluted aqueous sulfuric acid in THF. The mechanism of this reaction was investigated by 13C‐labelling of the starting compound 2. An Unusual C‐1‐‐C‐2 Ring‐Splitting of Pyranosides by a Retro‐Aldol Reaction – a Route to New Chiral Building Blocks