Formation and equilibration of d-fructosides and 2-thio- d-fructosides in acidified dimethyl sulfoxide: synthetic and mechanistic aspects

Abstract

A kinetic study of the reaction of ketoses and ketosides under catalysis with very dilute acid to produce the ketosyl carbonium ion is reported, and the subsequent reaction of this ion with alcohol and thiol nucleophiles has been studied. The relative reactivity of d-fructosides and 2-thio- d-fructosides is discussed, and some tentative conclusions have been reached on the mechanisms of their furanoside-pyranoside equilibration. The change in ring size in such systems probably proceeds via an anhydro- d-fructose intermediate, rather than an acyclic intermediate. The synthetic applications of the system have been explored, and it has been shown that both d-fructosides and 2-thio- d-fructosides may be synthesized in good yield. The d-fructofuranosides are best obtained from sucrose as the starting material, whereas the pyranosides are obtained from any readily available d-fructopyranoside ( e.g., methyl β) by use of the desired alcohol or thiol, only the β anomers being obtained. Three new 2-thio- d-fructosides are reported.