Contact ion pairs and solvent-separated ion pairs from d-mannopyranosyl and d-glucopyranosyl triflates

• Ion pairs from a mannosyl triflate donor were studied at the DFT(M06-2X) level of theory.
• Oxacarbenium ions from the mannosyl donor preferred B2,5-like conformations to 4H3-like ones.
• Dioxacarbenium ions with a 1,6-anhydro structure are more stable in the mannosyl series than in the glucosyl one.

The chemical nature of contact ion pairs and solvent-separated ion pairs from 2,3,4,6-tetra-O-methyl-α-d-mannopyranosyl triflate was investigated at the DFT(M06-2X) level of theory. Comparison of the present results to those obtained for the d-glucopyranosyl counterpart in our previous study indicated that the ion pairs from the d-mannopyranosyl triflate adopt B2,5-like conformations more preferably than those from the d-glucopyranosyl triflate. Similarly, 1,6-anhydro-d-mannopyranosyl dioxacarbenium ions bearing a 1C4 conformation were shown to be more stable than the d-glucopyranosyl counterparts.

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