Bromine‐Promoted Glycosidation of Conformationally Superarmed Thioglycosides

Abstract

Presented herein is a study of the conformation and reactivity of highly reactive thioglycoside donors. The structural studies have been conducted using NMR spectroscopy and computational methods. The reactivity of these donors has been investigated in bromine‐promoted glycosylations of aliphatic and sugar alcohols. Swift reaction times, high yields, and respectable 1,2‐cis stereoselectivity were observed in a majority of these glycosylations.

A Streamlined Regenerative Glycosylation Reaction: Direct, Acid‐Free Activation of Thioglycosides

“…In further expansion of the approach, we investigated conformationally super‐armed donor 32 [31] equipped with silyl protecting groups. Glycosidation of glucosyl donor 32 with acceptor 2 smoothly afforded the desired disaccharide 33 [31] in an excellent yield of 93 % with predominant α‐stereoselectivity (α/β = 5.0/1, entry 11). No loss of TBS protecting groups, which was noted as a major side reaction in our previous unrelated study, [31] was noted in NIS/HOFox‐promoted reactions.…”

“…Glycosidation of glucosyl donor 32 with acceptor 2 smoothly afforded the desired disaccharide 33 [31] in an excellent yield of 93 % with predominant α‐stereoselectivity (α/β = 5.0/1, entry 11). No loss of TBS protecting groups, which was noted as a major side reaction in our previous unrelated study, [31] was noted in NIS/HOFox‐promoted reactions. Glycosidation of relatively unreactive 2‐phthalimido‐protected aminosugar donor 34 [32] with electronically deactivated glycosyl acceptor 10 was also proven feasible.…”

“…In further expansion of the approach, we investigated conformationallys uper-armed donor 32 [31] equipped with silyl protecting groups. Glycosidation of glucosyl donor 32 with acceptor 2 smoothly afforded the desired disaccharide 33 [31] in an excellent yield of 93 %w ith predominant a-stereoselectivity (a/b = 5.0/1, entry 11).…”

“…Methyl 6‐ O ‐(6‐ O ‐benzoyl‐2‐ O ‐benzyl‐3,4‐di‐ O ‐ tert ‐butyldimethylsilyl‐α/β‐ d ‐glucopyranosyl)‐2,3,4‐tri‐ O ‐benzyl‐α‐ d ‐glucopyranoside (33) was obtained from thioglycoside 32 [31] and glycosyl acceptor 2 by the general glycosylation method as a colorless syrup in 93 % yield (α/β=5.0/1). Analytical data for 33 was in accordance with that reported previously [31] …”

“…Analytical data for 30 was in accordance with that reported previously. [29] 1-Adamantyl 2,3,4,6-tetra-O-benzyl-a/b-d-glucopyranoside (31) was obtained from thioglycoside 28 and 1-adamantanol 16 by the general glycosylation method as aw hite amorphous solid in 91 % yield (a/b = 1.0/1). Analytical data for 31 was in accordance with that reported previously.…”