Estimation of the Anomeric Effect of the Cyano Group

The anomeric effect1,2 is a well established phenomenon among carbohydrate derivatives, and more generally among 2-substituted tetrahydropyrans. The generalized anomeric effect1 refers to structural moieties R-X-C-Y (where X possesses one or two lone pairs of electrons, and Y is an atom or group of high electronegativity) in both open chain or cyclic molecules. Thus hydroxyacetonitrile prefers to exist in the gauche conformation,3,4 and several 3-cyano-perhydro-1,2-oxazine derivatives prefer conformations in which the C-3--CN bond and the lone pair of the nitrogen are coplanar.5 Investigation of conformational equilibria of all but one 2,6-anhydro-hexononitrile6,7 (pentopyranosyl cyanides) left doubt relating to the anomeric effect of the cyano group, and raised the possibility of a stabilizing interaction between 1,3-diaxial cyano and acetoxy groups.