Convenient Synthesis of Nucleoside and Isonucleoside Analogues

A very simple methodology to stereoselectively achieve tricyclic isonucleosides (nucleobase = thymine, uracil, and 5-fluoruracil) and 3‘-C-branched nucleosides (nucleobase = theophylline) was performed by means of a DBU-mediated addition process using a readily available
2-bromo sugar. The mechanism for these transformations implies the loss of both substituents at C-2 and C-3 on the sugar moiety, and
although it seems that DBU is probably involved, its involvement has not yet been ascertained. Cytosine did not react under these conditions.