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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Silica gel-supported ceric ammonium nitrate (CAN-SiO2) was found effective for rapid and selective cleavage of trityl (Tr), monomethoxytrityl (MMTr), and dimethoxytrityl (DMTr) groups from protected nucleosides and nucleotides under mild conditions. Efficiency of deprotections depended upon the stability of the resultant carbocationic species: DMTr+ > MMTr+ > Tr+. Use of a catalytic amount of this solid-supported reagent can also efficiently and selectively remove the tert-butyldimethylsilyl or the triisopropylsilyl group from a primary hydroxyl functionality in di- or trisilyl ethers of ribonucleosides. A comparative study of deprotection reactions by utilization of CAN alone or CAN-SiO2 indicates a remarkable increase in the rate of the reactions involving a solid support. The mechanism of electron-transfer processes is proposed for the use of CAN-SiO2 in the removal of these protective groups from organic molecules.