Abstract
The 3 disaccharides lactose, cellobiose and maltose in the form of their acetylated glycosyl bromides were reacted with 8-ethoxycarbonyloctanol to provide 1,2-trans-glycosides. Conventional Koenigs-Knorr and Helferich conditions provided these glycosides in poor yield but silver trifluoromethanesulfonate, N,N-tetramethylurea gave the disaccharide glycosides in 50-60% yield. Use of 2,4,6-trimethylpyridine as proton acceptor provided the corresponding 1,2-orthoacetates in 60-70% yield. These 1,2-orthoesters were rearranged by stannic tetrachloride to the 1,2-trans-glycosides. Isolation of acetylated 8-ethoxycarbonyloctanol from Lewis acid catalyzed isomerization of 1,2-orthoesters and from Koenigs-Knorr reactions in which N,N-tetramethylurea was the proton acceptor is discussed in terms of a reaction mechanism proceeding from glycosyl halide to glycosidic products via a 1,2-orthoester intermediate. 1H NMR indicated the presence of 1,2-orthoacetate in Koenigs-Knorr reaction mixtures and 1,2-orthoacetate was isomerized to glycoside by the conjugate acid of N,N-tetramethylurea. [This may be relevant to serological cross-reactions between pathogenic bacteria and antibody prepared against artificial carbohydrate antigens.].

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