Radical cyclisation reactions leading to polyhydroxylated cyclopentane derivatives: synthesis of (1R,2R,3S,4R)- and (1S,2S,3R,4S)-4-hydroxyethylcyclopentane-1,2,3-triol

The tetraol (–)-1 has been prepared from a derivative of (D)-allose 3. The stereoselective carbocyclization reaction (8⇒11) formed the key step in this sequence. The enantiomeric cyclopentane derivative (+)-1 was also prepared from compound 3. In this synthesis the cyclization of compound 18 to provide the carbocycle 19 features as the critical carbon–carbon bond forming reaction.