Monosaccharide 1,2-alkyl orthoesters are of considerable importance as precursors in the synthesis of glycosides and oligosaccharides1-4. For the preparation of orthoesters, Kochetkov and Bochkov2 have pointed out that acylglycosyl halides can be treated with an alcohol in the presence of silver oxide and carbonate. However, use of such acid acceptors result in the formation of water, which must be removed rapidly by dessicants to prevent the formation of by-products. 2,4,6-Trimethyl-and 2,6dimethyl-pyridine which, unlike quinoline and pyridine, do not react rapidly with glycosyl halides to form quaternary glycosylammonium salts because of steric hindrance of the nitrogenous component are preferable acid acceptors not giving rise to water. Variations on the latter approach have been the use of 2,4,6_trimethylpyridine_containing tetraalkylammonium bromide5, silver tri-flate6, or silver nitrate'. Orthoesters have also been prepared in high yield from appropriate reactants in dichloromethane containing N,N-dimethylformamide dialkyl acetal and silver triflate8.
The present investigation concerns a search for reactions that result in the formation of the simple alkyl 1,Zorthoesters of o-glucopyranose and o-galactopyranose in high yield, without formation of glycosides. One method, that of Zurabyan et aL7, seemed particularly promising since orthoesters of partially protected sugar derivatives were prepared by 1,2-cis acylglycosyl halides without apparent formation of glycosides. The reaction was carried out in acetonitrile in the presence of 2,4,6_trimethylpyridine and silver nitrate. In the following experiments, similar conditions were used in the treatment of 1,2-c& and 1,Ztrans halides with such simple alcohols as methanol, 2-propanol, and 1-octanol. In addition to silver nitrate, other silver salts were tested and the products analyzed, in terms of forma-*Portions of this work were presented by D. Tsui at the 185th Meeting of the American Chemical Society,