Synthesis of 5'-fluoro-2'-beta-methylneplanocin analogues (5) was carried out. The cyclopentenone 16 was prepared from methyl mannopyranoside by using ring closing metathesis, stereoselective introduction of methyl group, and seleno cyclization as representative steps. Introduction of a fluorine atom was conducted by electrophilic fluorination. Antiviral activity of 5 will also be presented.