A series of fused-bicyclic acetals containing a disiloxane ring was investigated to evaluate the source of selectivity in silyl-protected 2-deoxyribose systems. The disiloxane ring unexpectedly enables the diaxial conformer of the cation to be stabilized by an electronegative atom at C-3. This low energy conformer subsequently undergoes stereoelectronically controlled nucleophilic addition to give substituted tetrahydrofurans with high diastereoselectivity.