Defining the Scope of the Acid‐Catalyzed Glycosidation of Glycosyl Bromides

Abstract

Who designed the cover?We have been collaborating with Fabia D'Amore-Krug, at alented artist who teaches art therapy.F or our previous covers, all we had to do is describe the general outcome of our article in lay terms, and she would immediately come up with an image in her head. The fact that this reaction can now proceed much faster was shown by Fabia with two cars:o ld and slow versus new and fast. She quickly sketched the image of the two cars racing each other and came up with other ideas, such as gas stations, St. Louis skyline, etc. Fabia's initial sketch was done in pencil and then she created her final image in beautiful watercolor.

A Highly Efficient Glycosidation of Glycosyl Chlorides by Using Cooperative Silver(I) Oxide–Triflic Acid Catalysis

“…[16] Nevertheless, this result favorably compares to inefficient glycosylations of thioglycoside acceptors in our previous studies with glycosyl bromides as donors. [9][10] A very similar outcome was achieved with mannosyl donor 3. Thus, glycosylation of acceptors 4-7 afforded the corresponding disaccharides 24-27 in 30 min in 98-99% yield (entries 10-13).…”

“…These optimized conditions compare very favorably with those used for the glycosyl bromide activations, 0.50 equiv of silver(I) oxide and 0.35-0.40 equiv of TfOH. [10] Glycosylation of secondary acceptors 5-7 gave similar results. Thus, glycosylation of a relatively unreactive 4OH acceptor 5 afforded disaccharide 13 in 90% yield in 30 min (entry 2).…”

“…However, glycosylation of thioglycoside acceptors was somewhat inefficient in our previous studies with ferric chloride promoter [8] or with glycosyl bromides as donors. [9][10] In addition, these glycosylations could be prone to competing aglycone transfer reactions, [16] which was not observed in this case. 27, 99% a -all yields are isolated yields after column chromatography With notable success with glucosyl donor 1, we turned our attention to investigating benzoylated chlorides of the Dgalacto and D-manno series, 2 and 3, respectively.…”

“…[9] An effort dedicated to studying the reaction mechanism, made it possible to reduce the amount of Ag 2 O to only 0.50 equiv and replace TMSOTf with TfOH. [10] Although we achieved a significantly improved outcome of the Koenigs-Knorr-like glycosylation reactions, a few limitations and uncertainties remained. First, glycosidation of bromide donors containing the nitrogen atom such as derivatives of glucosamine were very slow and provided poor yields.…”

Stereoselective synthesis of alkyl pyranosides on a laboratory scale

“…Methanolyses of 2,3,4,6-tetra-O-acetyl--D-glucopyranosyl bromide in the presence of silver salts (e.g. silver(I)triflate) 26 or mercury salts (Königs-Knorr conditions) 27 have been widely used [28][29][30][31][32][33] . However, the use of silver salts for large scale preparations is expensive, and the use of mercury salts raises ecological concern.…”