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