SNCL4 VERSUS TICL4-MEDIATED COUPLING BETWEEN N-6-BENZOYLADENINE AND PERBENZOYLATED 2-DEOXYPYRANOSE - APPLICATION TO THE SYNTHESIS OF CERTAIN HOMOCHIRAL ACYCLONUCLEOSIDES AND CARBOACYCLONUCLEOSIDES

1,3,4-tri-O-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.