Efficient conversions of ribonucleosides into their 2',3'-anhydro,2'(and 3')-deoxy, 2'-3'-didehydro-2'-3'-dideoxy and 2'3'-dideoxynucleoside analogues

A general scheme for the transformation of ribonucleosides into the corresponding sugar-modified derivatives is presented. Mixtures of 2'-3'-bromohydrin acetates with different O5' substituents were formed from the reaction of purine, pyrimidine and mofidied purine ribonucleosides with 2-acetoxy-2-methylpropanoyl (alpha-acetoxyisobutyryl)bromide in acetonitrile. Reductive elimination with zinc-copper couple or zinc powder in the presence of acetic acid affords the formation of unsaturated-sugar nucleosides.