Novel Approaches for the Synthesis and Activation of Thio- and Selenoglycoside Donors

Abstract

Alkyl thio-, phenyl seleno-, and phenyl thioglycosides can be prepared through short synthetic sequences based on the generation of glycosyl iodides as versatile intermediates. In addition, a novel cheap combined system (stoichiometric NBS and catalytic Bi(OTf)3) has been developed for rapid and efficient activation of a wide variety of thio- and selenoglycoside donors.

Direct chemical glycosylation with pentenyl- and thioglycoside donors of N-acetylglucosamine

“…However, a significant drop in the yield and extension of the reaction time was observed for all three acceptors (12)(13)(14) despite them being primary alcohols. Diacetone galactose (12) could be GlcNAc-ylated in only 37% yield, whereas benzylated glucoside 13 gave a moderate glycosylation yield of 50%.…”

“…NIS/Cu(OTf) 2 -mediated direct GlcNAc-ylation of carbohydratebased acceptors (12)(13)(14) 30 was next investigated with the superior pentenyl donor system (Table 3, entries 13-15) and indeed found to be possible. However, a significant drop in the yield and extension of the reaction time was observed for all three acceptors (12)(13)(14) despite them being primary alcohols.…”

New Principles for Glycoside‐Bond Formation

“…[72] Thioglycosides have also been activated with other halonium systems; for example, a cheap bromonium system (stoichiometric NBS and catalytic Bi(OTf) 3 ) was used to activate various thioglycoside donors. [73] Commercially available 1-fluoropyridinium triflates successfully promoted the transformation of thioglycosides into O-glycosides. [74] In the past decade, organosulfur compounds have become valuable promoters for thioglycoside activation: Early studies were devoted to sulfonium or sulfenyl triflates, such as DMTST, MeSOTf, and PhSOTf; more recently, sulfenamide activators in combination with Lewis acids such as EtSNPhthTrB(C 6 F 5 ) 4 [75] and N-(phenylthio)-e-caprolactam-Tf 2 O [76] were proposed.…”

An Easy and Versatile Approach for the Regioselective De‐O‐benzylation of Protected Sugars Based on the I2/Et3SiH Combined System

“…[21] An analogous stoichiometric combination of these reagents in methanol was found to be effective for the cleavage of benzylidene acetals. [22] Additionally, stoichiometric amounts of both I 2 and Et 3 SiH allow glycosyl iodides to be generated from 1-O-acylated precursors within a few minutes; this rapid process has been incorporated into several procedures, which have lead to a variety of useful saccharide intermediates, such as 1,2-orthoesters, [23] ethylidenes, [23] glycals, [23] thio-and selenoglycosides, [24] and 2-O-deprotected allyl glycosides, [25] as well as glyco-conjugates with estradiol [26] or melanogenic 5,6-dioxyindole. [27] Additional synthetically useful applications of I 2 /Et 3 SiH have been reported by other groups for the regioselective reductive ring opening of benzylidenes, [28] the reductive Ferrier rearrangement of glycals [29] and the Friedel-Crafts cyclisation of aryl-substituted propargyl alcohols.…”