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 alpha-oxoketene dithioacetal sugar derivatives 2 and 7 with concentrated hydrochloric acid in THF leads to the open-cha in uloses 3 and 8. The reaction mechanism can be rationalized as a ret ro-aldol reaction. This rationalization was supported by reacting 2 an d 7 with DCl/D2O. Compound 3 was converted into the chiral pyrazoles 1 2 and 13. The branched-chain ulose 2 forms the thiopyranosidulose 15 w hen treated with diluted aqueous sulfuric acid in THF. The mechanism o f this reaction was investigated by C-13-labelling of the starting com pound 2.