Analysis of permethylated hexopyranosyl-2-acetamido-2-deoxyhexitols by g.l.c.-m.s.

The major product obtained on acetonation of d-mannose with a 2-molar excess of isopropenyl methyl (or ethyl) ether is 4,6-O-isopropylidene-α-d-mannopyranose (3a), the product of kinetic acetonation: a larger excess of the reagent leads, to the 2,3:4,6-diisopropylidene acetal (6). The course of the reaction and side-products formed were examined in detail. The 1,2,3-triacetate of 3a was deacetonated to give α-d-mannopyranose 1,2,3-triacetate; similar reactions were performed on the β anomers. The 1-acetate of the diacetal 6 could be selectively deacetonated to give 1-O-acetyl-2,3-O-isopropylidene-α-d-mannopyranose. The reactions provide access to protected derivatives of d-mannose, and partially acylated derivatives, having modes of substitution different from those obtainable by classical acetonation procedures conducted under conditions of thermodynamic control.