Showing papers on "Koenigs–Knorr reaction published in 2003"

2,3-Anhydrosugars in glycoside bond synthesis. NMR and computational investigations into the mechanism of glycosylations with 2,3-anhydrofuranosyl glycosyl sulfoxides

Abstract: We report here the combined use of computational chemistry and low-temperature NMR spectroscopy to probe the mechanism of a highly stereoselective glycosylation reaction employing 2,3-anhydrofuranosyl glycosyl sulfoxides (2 and 4). The reaction involves a two-step process that is carried out in one pot. In the first step, the sulfoxide is reacted with triflic anhydride leading to the formation of a single intermediate. Using NMR spectroscopy, we have established the structure of this intermediate as a glycosyl triflate. In the second step, the acceptor alcohol is added to the reaction mixture, which leads to the highly stereocontrolled formation of the glycoside product. The structure of the major product is consistent with a pathway involving an SN2-like displacement of the triflate by the alcohol. In the predominant intermediate that is formed, there is a trans relationship between the triflate group and epoxide. Therefore, in the glycoside product there is a cis relationship between the epoxide and the...