Procedures have been developed for the selective formation of (a) 2′,5′-silylated ribonucleosides and (b) 3′,5′-silylated ribonucleosides. These procedures also permit the selective silylation at either the 2′- or 3′-position of dimethoxytritylated ribonucleosides. The procedures involve nitrate or perchlorate ion catalysis for selective reaction at 2′-positions and a combination of silver ion and DABCO or 4-nitropyridine N-oxide for selective reaction at the 3′-position. During the course of this work a general and rapid procedure was developed for the preparation and isolation of the 5′-dimethoxytrityl derivatives of the four common ribonucleosides. Silver ion was found to have a marked effect on dimethoxytritylation reactions.

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A general procedure is described for the preparation of protected arabinonucleosides. Protection at the 5′-position involves triphenylmethyl groups (DMT and MMT) while the tert-butyldimethylsilyl (TBDMS) group is used to protect the 2′- or 3′-positions. The effects of novel catalysts on the position of silylation have been determined, leading to highly selective reactions at 2′- or 3′-positions.

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