Mitsunobu Transformations of 1,2-O-Isopropylidene-α-D-pentofuranoses Mediated by Zinc Salts

A one-pot regioselective heterofunctionalization of 1,2-O-isopropylidene-α-D-xylofuranose (1) and 1,2-O-isopropylidene-α-D-ribofuranose (2) with zinc azide, zinc thiocyanate or zinc N,N-dimethyldithiocarbamate via the Mitsunobu reaction has been performed. With 2, the reaction gave selectively 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 predominant formation of a cyclic 3,5-anhydro derivative. In contrast, the reaction of hydrazoic acid with 1 afforded 5-azido-5-deoxy-1,2-O-isopropylidene-α-D-xylofuranose besides formerly unknown 5-azido-3,5-dideoxy-1,2-O-isopropylidene-α-D-glycero-pent-3-enofuranose and 3,5-diazido- 3,5-dideoxy-1,2-O-isopropylidene-α-D-ribofuranose; the yields depended on the reaction time and the molar ratio of reagents.