The reaction of 2′,3′-O-isopropylidene protected purine nucleosides with diisobutylaluminum hydride (DIBAL-H) caused the reductive cleavage of the C-1′O-4′ bond to give the corresponding 9-d-ribitylpurines. The ring cleavage of inosine 1a, thioinosine 1f, and their derivatives having an alkyl group at the O6- or S6-position 1c,e, and g proceeded smoothly to afford the corresponding ribityl derivatives