New catalysts and procedures for the dimethoxytritylation and selective silylation of ribonucleosides

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.