Stereoselective synthesis of l-isonucleosides

l-Isonucleosides 17 and 19 were stereoselectively synthesised from (S)-glycidol by two different procedures. The key step was the synthesis of a chiral dihydrofuran which was carried out by oxidation/elimination of 8 and by ring-closing metathesis of diene 10. The procedure can be applied to the synthesis of both enantiomers.