The Wittig condensation of the bicyclic lactol (I) with 4-(methoxycarbonyl)butyl triphenylphosphonium bromide (II) by means of sodium methylsulfinyl carbanide in DMSO and simultaneous dehydrobromination gives the bis(tetrahydropyranyl) derivative (III), which is finally deprotected by a treatment with oxalic acid in refluxing acetone.