Nucleophilic displacement reactions of some carbohydrates in dimethyl sulphoxide

Several 5-0-toluene-p-sulphonyl and 5-iodo
derivatives of «-and 3-ribofuranoses and «-xylofuranose
have been prepared in order to study their reactions
with sodium hydrogen carbonate in dimethyl sulphoxide.
Similar reactions are known to convert acylic primary
sulphonates and iodides to aldehydes but the sugar
derivatives were observed to yield different products.
Detosylation of the sugars to give the corresponding
alcohols was the most usual outcome but in two instances
the tosyloxy and iodo groups were ejected to give an
anhydro sugar and a rearranged product respectively. The
mechanisms of these reactions are considered.
Reaction of a ribofuranose primary sulphonate with
the anion of dimethyl sulphoxide led to base-induced
elimination of toluene-p-sulphonic acid rather than
nucleophilic substitution.
The results of the work are presented within the
context of possible approaches to converting pentoses
into hexoses by way of chain extension reactions at the
C-5 carbon atom of pentofuranoses.