The total synthesis of (-)-trans-kumausyne has been accomplished in an enantiospecific fashion starting from an L-arabinose derivative. The key step is the stereoselective formation of the substituted tetrahydrofuran via novel cyclization of the beta-silyl cation intermediate, generated by the addition of allylsilane to di-O-isopropylidene-aldehydo-arabinose in the presence of boron trifluoride etherate.