Medium-Controlled Intramolecular Catalysis in the Direct Synthesis of 5′-O-Protected Ribonucleoside 2′- and 3′-Dialkylphosphates

Electrophilic participation of the cis‐vicinal hydroxyl group accelerates the synthesis of the title compounds (see scheme). The aprotic, organic solvent induces a hydrogen‐bonded intermediate, thus providing a different phosphoryl transfer mechanism to the nucleophilic pathway observed in aqueous media.