Anomeric Effect of the Nitrogen Atom in the Isocyano and Urea Groups

Abstract The anomeric effect associated with the nitrogen atom in the isocyano group was investigated by using 1H NMR spectroscopic analysis of an anomeric pair of xylopyranosyl isocyanides 8 and 7. We found that β‐anomer 7 prefers to exist in the 1C4 conformation in which the nitrogen atom in the isocyano group adopts an axial orientation. This observation, coupled with the results of X‐ray crystallographic analysis establishes that the nitrogen atom in the isocyano group displays the anomeric effect. Furthermore, xylopyranosyl isocyanides 8 and 7 were transformed into the corresponding xylopyranosyl ureas 10 and 11. In the case of the urea group, a normal sterically determined preference is observed in which the bulky urea substituents at the pyranose anomeric position occupy the equatorial position.