SnCl4 versus TiCl4-mediated coupling between N-6-benzoyladenine and perbenzoylated 2-deoxypyranose: Application to the synthesis of certain homochiral acyclo and carboacyclonucleosides

1,3,4-tri- -benzoyl 2-deoxyribopyranose and persilylated N-6-benzoyladenine react in two different and regioselective ways according to the nature of the coupling reagent SnCl₄ or TiCl₄. The former Lewis acid gives rise to the anomeric mixture of N-9 nucleosides and the latter affords mainly 3′-deoxy 3′-(N-6-benzoyl-9-adenyl) glycals. These two series of derivatives constitute useful synthons for the preparation of homochiral acyclo and carboacyclonucleosides.