Convenient syntheses of substituted pyranoid glycals from thiophenyl glycosides and glycosyl phenylsulfones

A simple access to 3,6-branched oligosaccharides: Synthesis of a glycopeptide derivative that relates to Lycium barbarum L.

“…The armed-disarmed strategy 8 was next investigated using isopropyl thioglactopyranoside glycosyl donor 18 and NIS-TMSOTf as catalyst. When armed donor 18 was regioselectively glycosylated with disarmed acceptor thioglycoside 21 9 in anhydrous methylene dichloride-diethyl ether (1 : 1, v/v) co-solvent, α-linked disaccharide 22 was obtained in an isolated yield of 62% after recovery of 60 mg of 21 (see Experimental section). Glycosylation of 18 and acceptor 23 in diethyl ether, on the other hand, furnished disaccharide 24 in 96% yield as a mixture of the αand β-anomer in the ratio of 2 : 1.…”

“…1.04 g of phenyl 4,6-O-benzylidene-1-thio-β--galactopyranoside 9 (2.86 mmol) was dissolved in 10 mL of pyridine, then premixed benzoyl chloride (2.2 mL, 18.5 mmol) and pyridine (3 mL) was added; the mixture was stirred vigorously at 50 ЊC overnight, and then poured into ice-cold water, and extracted with CH 2 Cl 2 (2 × 30 mL). The organic phase was concentrated to dryness by repeated co-evaporation with toluene.…”

The Julia Reaction

“…Before 1990, this reaction was mostly effected using Na(Hg) amalgam. However, examples involving other reducing systems had already been reported, such as RMgX/Pd, Fe or Ni catalyst [58,[81][82][83][84]; Bu 3 SnH [21,[84][85]; Li naphthalenide [88][89][90]; Li or Na in liquid ammonia or in ethylamine [91,92]; Na 2 S 2 O 4 [93]; Raney nickel [94]; potassium graphite [95]; electroreductive reactions [96]; Te/NaBH 4 [97]; Al(Hg) amalgam and LiAlH 4 , with or without CuCl 2 [11,[98][99][100][101]. In 1990, Kende successfully employed samarium diiodide for the reductive elimination of b-hydroxy imidazolyl sulfones [102].…”

Synthesis of Pyranoid and Furanoid Glycals from Glycosyl Sulfoxides by Treatment with Organolithium Reagents

“…[22] In spite of the ready availability of glycosyl halides, their rather sensitive natures have led to the consideration of the more stable 1-thio-and 1-sulfonylglycosyl derivatives (e.g., 3, Scheme 1b) as glycal precursors. Compounds 3 are thus conveniently transformed into glycals when treated with lithium naphthalide, [23] chromium(II) complexes in aqueous medium, [24] or SmI 2 . [14,25] In the last case, electron transfer to the glycosyl phenylsulfone to generate a 1-glycosyl radical has been proposed; a (glycosyl)samarium deriva-tive would then be formed, [14,25] with subsequent β-acetate elimination resulting in the formation of the expected glycal.…”