2,3-Anhydrosugars in glycoside bond synthesis. Application to the preparation of C-2 functionalized α-d-arabinofuranosides

General Aspects of the Glycosidic Bond Formation

“…More recently, a notable improvement in stereoselectivity of 1,2-cis furanosylation was achieved by using glycosyl donors in which the ring has been locked into a single conformation. These examples include 2,3-anhydro [165][166][167][168][169], 3,5-O-(di-tert-butylsilylene) [170,171] and 3,5-O-tetraisopropyldisiloxanylidene [172] protected bicyclic glycosyl donors.…”

2,3-Anhydrosugars in Glycoside Bond Synthesis. Application to 2,6-Dideoxypyranosides

“…For example, glycosylation of alcohols with 1 upon treatment with N-iodosuccinimide and silver triflate leads to the highly stereoselective formation of 2,3-anhydrosugar glycosides (4) in which the newly formed glycosidic bond is cis to the epoxide moiety. [1][2][3][4][5][6][7] Alternatively, glycosylation of alcohols with 1 in the presence of a Lewis acid leads to the formation of 2-deoxy-2-thiotolylglycosides 5, which are precursors to 2-deoxy glycosides 6. 8 The latter glycosylation also proceeds with a high degree of stereocontrol, which by analogy to other similar migration-glycosylation processes, [9][10][11][12][13][14][15][16][17][18] we attributed to the formation of episulfonium ion intermediate (e.g., 7).…”

“…8 The latter glycosylation also proceeds with a high degree of stereocontrol, which by analogy to other similar migration-glycosylation processes, [9][10][11][12][13][14][15][16][17][18] we attributed to the formation of episulfonium ion intermediate (e.g., 7). In all of our previous studies, [1][2][3][4][5][6][7][8] the donors employed were in the furanose ring form, and we were curious as the potential of their pyranoside counterparts (e.g., 8 and 9) in these reactions, particularly in the preparation of 2,6-dideoxysugar glycosides. 2,6-Dideoxypyranosides are an important class of carbohydrates, which are present as essential components of steroidal glycosides, antibiotics, and antitumor compounds.…”

“…1H, J 2,3 ) 3 5. Hz, H-3), 3.41 (d, 1H, J 2,3 ) 3.5 Hz, H-2), 2.36 (s, 3H, tolyl CH 3 ), 1.27 (d, 3H, J 5,6 ) 6.2 Hz, 3 × H-6);…”

2,3-Anhydrosugars in Glycoside Bond Synthesis. Application to α-d-Galactofuranosides

“…In previous reports, we have described the use of 2,3-anhydrosugar thioglycosides and glycosyl sulfoxides in the stereocontrolled synthesis of oligosaccharides containing arabinofuranosyl residues. − Glycosylating agents 1 and 2 (Figure ), upon coupling with a range of different alcohols, provide glycosides with the 2,3-anhydro-β- d - lyxo stereochemistry (e.g., 3 ), which in turn can be converted to β-arabinofuranosides (e.g., 4 ) by reaction with lithium benzylate (BnOLi) in the presence of (−)-sparteine followed by deprotection. , Analogously, donors 5 and 6 give α-arabinofuranosides (e.g., 8 ) via 2,3-anhydro-α- d -ribofuranosides (e.g., 7 ); however, in these cases, the additive is not necessary in the epoxide-opening step . The method has also been applied to the synthesis of nucleosides…”