Conformational effects in 2‐deoxyglucopyranos‐1‐yl radicals

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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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