REACTION OF SUGAR EPOXIDES WITH PHOSPHOROTHIOIC ACIDS, EVIDENCE OF THE PENTACOORDINATE PHOSPHORUS INTERMEDIATE IN THE REACTION OF 5,6-ANHYDRO-1,2-O-ISOPROPYLIDENE-α-D-GLUCOFURANOSE WITH PHOSPHOROTHIOIC ACIDS

Article abstract of DOI:10.1016/S0040-4020(01)87463-9

The reaction of sugar epoxides with organic monothioacids of phosphorus provides a convenient procedure for synthesizing sugar thiophosphates and mercaptosugar phosphates.Based on detailed analysis of intermediates and factors influencing the reactivity of phosphorus monothioacids with sugar epoxides the reaction scheme is proposed involving pentacoordinate intermediate which undergoes endo or/and exocyclic elimination.It was found that the reaction of 5,6-anhydro-1,2-O-isopropylidene-α-D-glucoforanose 7 with phosphorothioic acids 8a and 8b yields three types of products in equilibrium: the thiophosphates 9a and 9b, the oxathiaphospholanes 11a and 11b and the mercaptophosphates 10a and 10b.Under more drastic conditions the phosphates 10a and 10b can be converted irreversibly into the episulphide 12 and phosphoric acids 13a and 13b, respectively.It is clearly possible that both compounds 10 and 11 can be formed from the same pentacoordinate intermediate, and the experimental evidence provides strong support for it.