Glycosylation with Disarmed Glycosyl Bromides Promoted by Iodonium Ions

Abstract

Iodonium ions have been developed for activating glycosyl bromides in the coupling to glycosyl acceptors. The iodonium ions are generated from N-iodosuccinimide and a protic acid such as camphorsulfonic acid or triflic acid, where the latter gives the most reactive promoter system. The couplings occur with the release of iodine monobromide and the best results are obtained with benzoylated glycosyl donors and acceptors. In this way, disarmed glycosyl bromides can serve as glycosyl donors without the use of heavy metal salts.

O-Glycosylation Enabled by N-(Glycosyloxy)acetamides

“…The reaction of donor 17 (24.1 mg, 0.036 mmol) and acceptor 8 (12.1 mg, 0.026 mmol) was performed as described in the general procedure C, affording 15 (24.6 mg, 91% yield). The 1 H NMR data for 15 are in accordance with those reported previously …”

“…The 1 H NMR data for 15 are in accordance with those reported previously. 36 Methyl 3,4,6-Tri-O-benzyl-2-O-(2,3,4,6-tetra-O-benzoyl-β-D-galactopyranosyl)-α-D-glucopyranoside (37). The reaction of donor 7 (24.1 mg, 0.036 mmol) and acceptor 36 (12.1 mg, 0.026 mmol) was performed as described in the general procedure B, affording 37 (eluent: petroleum ether/ethyl acetate = 5:1 (v/v); 24.4 mg, 90% yield).…”

Koenigs–Knorr Glycosylation Reaction Catalyzed by Trimethylsilyl Trifluoromethanesulfonate

“…To advance the classical Koenigs-Knorr glycosylation, many activators including salts of mercury, [5][6][7][8] cadmium, [9][10][11] tin, [12,13] zinc, [14,15] indium, [16,17] silver [18][19][20][21][22][23][24][25][26] have emerged. [27] Nevertheless, these modifications failed to adequately enhance the reactiont hat continued to suffer from fair yields, poor reactivity of donors, substrate scope, and the requirement to use excess of toxic or expensive reagents.T his prompted the investigationo fo ther,n on-metallic activators andp romoters including halide ions, [28] iodine or IBr with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone/1,4-diazobicyclo[2.2.2]octane( DDQ/DABCO), [29,30] bromine, [31] and 3,3-difluoroxindole (HOFox), [32,33] diarylborinic acid, [34] iodonium ions, [35] halogen bonding, [36] supercriticalC O 2 , [37] and organocatalysis. [38][39] Many of these conditions still fail to glycosidate perbenzoylated bromides.…”

Phenanthroline‐Catalyzed Stereoretentive Glycosylations

“…To initiate our investigation, the α‐glycosyl bromide 1 was chosen as a model electrophilic partner and the galactopyranoside 2 as a nucleophile to simplify the analysis of coupling product mixtures (Table ). Previous reports have documented the ability of glycosyl bromides to function as effective electrophiles under various reaction conditions . The reaction of 2 with 1 , having a C2 benzyl (Bn) group, often proceeds by an S N 1‐like pathway.…”