Mitsunobu transformations of 1,2-O-isopropylidene-alpha-D-pentofuranoses mediated by zinc salts

A one-pot regioselective heterofunctionalization of 1,2-O-isopropylidene-al pha -D-xylofuranose (1) and 1,2-O-isopropylidene-alpha -D-ribofuranose (2) with zinc azide, zinc thiocyanate or zinc N,N-dimethyldithiocarbamate via t he Mitsunobu reaction has been performed. With 2, the reaction gave selecti vely the desired products substituted at C-5 in good isolated yields (60-65 %). However, application of the same reaction conditions to 1 led to the pr edominant formation of a cyclic 3,5-anhydro derivative. In contrast, the re action of hydrazoic acid with 1 afforded 5-azido-5-deoxy-1,2-O-isopropylide ne-alpha -D-xylofuranose besides formerly unknown 5-azido-3,5-dideoxy-1,2-O -isopropylidene-alpha -D-glycero-pent-3-enofuranose and 3,5-diazido-3,5-did eoxy-1,2-O-isopropylidene-alpha -D-ribofuranose; the yields depended on the reaction time and the molar ratio of reagents.