Circular dichroism of 1,3-dioxane-type (2'-naphthyl)methylene acetals of glycosides.
The CD spectra are reported for a series of 1,3-dioxane-type 4,6-O-(2'-naphthyl)methylene acetals of carbohydrates with and without interacting aromatic protective groups on the C-1, C-2, and C-3 hydroxy groups. In the absence of interacting chromophores, the signs of the (1)B transitions are not sensitive to the configuration of C-4, while the signs of the weak (1)L(a) bands are opposite in the galacto and gluco derivatives. The equatorial parallel conformation is found to be the preferred conformation of the 2-naphthyl group in the solid state by X-ray diffraction. The intense (1)B(a) and (1)B(b) transitions of the naphthalene chromophore allowed a safe configurational assignment by exciton coupled interaction with the aromatic protective groups in para-methoxyphenyl-beta-D-glycosides. The origin of the observed CEs were deduced and the additivity of the interactions was studied. The direction of the hydrogenolytic cleavage of 4,6-O-(2'-naphthyl)methylene acetal of carbohydrates could also be detected by the (1)B(b) transition of the 2-naphthyl chromophore.