Ribonucleosides, rearrangement

A. Koch, C. Lamberth, F. Wetterich, and B. Giese, Radical rearrangement of 2-0-(di-phenylphosphoryl)glycosyl bromides. A new synthesis for 2-deoxy disaccharides and 2-deoxy ribonucleosides, J. Org. Chem., 58 (1993) 1083-1089. 

Protection of yie-diols. Several laboratories have recently reported migration of t-butyldimethylsilyl protective groups of ribonucleosides, Thus the 2 - and 3 -0-l-butyldimethylsilyl derivatives of ribonucleosides can rearrange in the presence of base (pyridine) by an intramolecular reaction. Obviously care must be exercised in the use of silicon-containing reagents for partial protection of polyols. 

Heating the imidazole ribonucleoside (656) with acetic anhydride and pyridine produced (657). Propionic anhydride reacted comparably (75JOC2920). The same ring system can be prepared by treating uric acid (658) with isobutyric anhydride. Cleavage and rearrangement... 

In a study of the partial protection of nucleosides, it was shown that acylation of a ribonucleoside with 1.2-1.5 equivalents of an acyl chloride in pyridine gave mostly the 2 -0-acyl isomer. Use of 2.2-3.0 equivalents of acyl chloride gave mostly the 2, 5 -di-0-acyl derivative, which rearranged over silica to the 3, 5 -diacyl... 

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