The reaction of tert-butyldimethylsilyloxy-sporogen-AOI (I) with phenylselenyl trifluoroacetate (II) gives the adduct (IIIa-b), which is treated first with MCPBA and then with K2CO3 in methanol to yield compound (IV). The Sharpless asymmetric epoxidation of (IV) with D-(-)-diisopropyl tartrate, Ti(OiPr)4 and tBu-OOH affords the mixture of diepoxides (Va)+(Vb), which is silylated with TBDMSCl and imidazole to the disilylated mixture of diepoxides (VIa)+(VIb). Finally this mixture is separated by column chromatography, and the desired diastereomer submitted to desilylation with TBAF to furnish the target compound.