Abstract
2-Unsubstituted and 2-substituted (fluoro, tosylamino, n-propyl) 3,4,6-tri-O-acetyl-2-deoxypyranosyl radicals are obtained by reaction of the corresponding pyranosyl bromides or phenylselenides with photolytically generated trimethyltin radicals in benzene solution. Analysis of the ESR hyperfine splittings reveals that the 2-deoxy-2-fluoroglucopyranosyl radical exists in a boat-like conformation at room temperature, whereas the others retain the 4C1 chair conformation of the starting material. The observed conformational effects are explained by a “quasi-homo-anomeric” frontier orbital interaction of the nx lone pair of the ring oxygen atom with the σ* MO of the β-C-O bond, in which the singly occupied p orbital at C-1 acts as a mediator for this 1,3-anomeric interaction.
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