Synthesis and characterization of some anomeric pairs of per-O-acetylated aldohexopyranosyl cyanides (per-O-acetylated 2,6-anhydroheptononitriles). On the reaction of per-O-acetylaldohexopyranosyl bromides with mercuric cyanide in nitromethane

The synthesis and characterization of the anomeric pairs of the per-O-acetylaldohexopyranosyl cyanides of D-galactose, L-fucose, D-glucose, and D-mannose, as well as of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl cyanide, are described. Cyanation of the readily available, per-O-acetylaldohexopyranosyl bromides with mercuric cyanide in nitromethane, and subsequent purification, gave the corresponding, crystalline glycosyl cyanides with a high degree of 1,2-trans stereoselectivity. Thus, per-O-acetylated aldohexopyranosyl cyanides of the 1,2-trans configuration were obtained in yields ranging from 20 to 79%, whereas the corresponding 1,2-cis anomers were obtained in yields of less than or equal to 8.4%, the ratios of the 1,2-trans:1,2-cis anomers so prepared being greater than or equal to 8.5:1. The principal by-products of these irreversible, cyanation reactions were the per-O-acetylated 1,2-O-[1-(exo- and endo-cyano)ethylidene]aldohexopyranoses, obtained in yields of up to 40%. The structural assignments of the per-O-acetylaldohexopyranosyl cyanides were unequivocally established by elemental analysis, chemical transformation, vibrational spectroscopy, and 13C- and 1H-nuclear magnetic resonance spectroscopy. Correlations between the physical properties and the anomeric configurations of these C-aldohexopyranosyl compounds are described.