2-Deoxy-2-iodo- and 2-Deoxy-2-bromo-α-glucopyranosyl Trichloroacetimidates:  Highly Reactive and Stereoselective Donors for the Synthesis of 2-Deoxy-β-glycosides

Abstract

[formula: see text] 2-Deoxy-2-iodo- and 2-deoxy-2-bromoglucopyranosyl trichloroacetimidates 8-10 and 22 are extremely useful precursors of 2-deoxy-beta-glycosides. These reactive glycosyl donors undergo highly stereoselective glycosidation reactions at -78 degrees C with a range of glycosyl acceptors using TBS-OTf as the activating agent. beta-Glycosides are obtained with > or = 19:1 selectivity in six of the seven examples reported herein.

Stereoselective Synthesis of α‐Linked 2‐Deoxy Glycosides Enabled by Visible‐Light‐Mediated Reductive Deiodination

“…further demonstrated that the iodo‐substituent at the C‐2 position well controlled the stereochemistry of the newly formed glycosidic bond 11. This character was further illustrated in the glycosylation of 2‐deoxy‐2‐halo‐glycosyl trifluoroacetimidtaes,8a trichloroacetimidates,12a–c thioethers,12d,e and fluorides,12f,g which provided the corresponding 2‐deoxy‐2‐halo‐glycosides, and after reductive removal, the 2‐deoxy‐glycosides with high stereroselectivity. Meanwhile, the use of oxidative coupling of glycals in the preferential synthesis of 2‐deoxy‐2‐halo‐α‐glycosides was developed by Lemieux,13a Tatsuta,13b Thiem,13c,d Kessler,13e and Danishefsky,13f respectively.…”

Stereoselective Formation of 2‐Deoxyglycosidic Bonds in Biologically Active Natural Products

“…In other studies, Roush et al reported that the glycosylations of 2-deoxy-2-halo-glycosyl trichloroacetimidates 65 or fluorides 66 also provided the corresponding 2-deoxy-2halo-glycosides with high stereoselectivities. In addition, the stereoselective synthesis of the 2,6-dideoxytetra and trisaccharide unit of durhamycins A and B (Figure 38 A new stereoselective glycosylation method using 2deoxy-2-iodo-thioglycosides, which was prepared by the Wittig-Horner olefination of a protected pentose derivative and subsequent I þ induced cyclization, was recently developed by D ıaz et al (Scheme 38.29).…”

Glycosyl Sulfonates Beyond Triflates

“…[9,10] This typically led to non-selective reactions, unless the donors were pre-modified with a temporary directing group at the C-2 position. [11] In an effort to overcome this need for temporary prosthetic groups, we reasoned that a less reactive leaving group at the anomeric position of the activated sugar donor intermediate would possess more covalent character then a triflate, which could favor S N 2 pathways. After several failed attempts to generate the glycosyl tosylate from a variety of donors, we turned our attention to direct activation of a hemiacetal.…”