No abstract

No abstract

No abstract

The reaction of 3,5,6-tri-O-benzoyl-1,2-O-isopropylidene-or-D-glucose with ethanethiol in the presence of hydrogen chloride gives a crystalline product in 60% yield as was first described in 1932. This product is now shown to be 4,5,6-tri-O-benzoyl-2,3-di-S-ethyl-2,3-dithio-D-allose diethyl dithioacetal. A mechanistic outline for the reaction is proposed.DURING investigations of the reaction of peracylated acyclic sugars in the carbonyl form with ethanethiol in the presence of acid catalysts we have observed replacement of acyloxy-groups in addition to diethyl dithioacetal formation, and, in an effort to understand the nature of the replacement processes, have studied the structure of the tetrathio-product (I) known to be formed on treatment of 3,5,6-tri-O-benzoyl-1 ,2-O-isopropylidenea-D-glucofuranose (11) under the same c0nditions.l Although the tetrathio-derivative has been known for 40 years it has apparently not been subjected to full analysis despite the unlikely validity of the originally suggested structure (3,5,6-tri-O-benzoyl-2,4-di-S-ethyl-2,4-dithio-~-glucose diethyl dithioacetal) . A considerable body of information reported in recent years indicates that ester migrations,2 neighbouring group participat i o n ~, ~~~ and configurational inversions might have been expected to occur during the reaction, and we now report justification for these expectations.The n.m.r. spectrum of compound (I) showed it to contain three benzoyl groups, four ethylthio-groups, and seven chain protons, and therefore that the structure was at least isomeric with that originally suggested.l The acetal proton resonance was readily assignable as the only doublet in the spectrum, and the signals derived from the other two protons attached to sulphurbonded carbon atoms were recognisable from their characteristic high-field positions.5 From the observa-

No abstract