Treatment of purine, pyrimidine, and modified purine (antibiotic) ribonucleosides with 2- acetoxy-2-methylpropanoyl (a-acetoxyisobutyryl) bromide in acetonitrile gave mixtures of 2', 3'-bromohydrin acetates with different 05 'substituents. Significant amounts of 5'-unprotected (hydroxyl) bromo acetates were obtained in some cases, and formation of 2 ', 3'-0- isopropylidene derivatives as minor byproducts was detected for the first time. Acid- ...