A Ramberg-Bäcklund approach to exo-glycals

A New Route toexo-Glycals Using the Ramberg−Bäcklund Rearrangement

“…Due to the long‐standing interest in sulfone and Ramberg−Bäcklund chemistry within our own research group,13 we also recognised the potential of such compounds: we envisaged a thioglycoside S , S ‐dioxide (glycosyl sulfone) being subjected to a Ramberg−Bäcklund rearrangement to introduce an exo ‐C−C double bond at the anomeric position (Scheme ). Initial studies established that this was indeed a feasible transformation, the scope of which appeared considerable with regard to both the saccharide and aglycon portions 14. Shortly after we disclosed our own results, similar findings were reported by Belica and Franck 15.…”

DBU assisted expeditious synthesis of glycosyl dienes via glycosylated β-hydroxy esters

“…Found: C,65.90;H,6.12;N,3.11. 7,173.5 (C@O),154.5,137.4,134.3,128.8,128.7,128.2,128.1,120.0,119.4 (ArC) 5, 128.8, 128.7, 128.2, 128.1, 126.9, 125.4, 125.1, 124.9, 124 8 Hz,1H,1H,1H,1H,, 4.16-4.09 (m, 2H, OCH 2 Me), 3.94, 3.92 (each s, each 1H, H-3), 3.70-3.65 (m, 1H, H-6), 3.32,3.13 (s,3H,OMe), 2.90 (br s, 1H, OH), 1.40, 1.35 (s, 6H, CMe 2 ), 1.16 (m,3H,Me). 13 C NMR (50 MHz, CDCl 3 ): d 173.…”

“…A soln of the above methanesulfonyloxy derivative and DBU (0.17 mL, 100 mol %) in anhydr toluene (5 mL) was refluxed at 130°C for 3 h. The reaction mixture was cooled, the solvent evaporated and the residue was dissolved in EtOAc (2 · 25 mL) and washed with water (2 · 12.5 mL). The organic layer was dried (Na 2 SO 4 ) and evaporated under diminished pressure to give a residual mass (0.35 g) which was chromatographed over SiO 2 column using a gradient of hexaneEtOAc (19:1!9:1) to give 4a (0.18 g, 36%) as a colourless foam; 7,137.4,136.8,132.4,132.3 (PyC),130.7,128.9,128.9,128.4,128.3,123.4 (PyC), 127.6 (ArC), 115.3 (CMe 2 ), 108.6 (C-1), 102.8 (C-7), 96.1 (C-…”

“…4 The enantioselective cycloaddition reactions have generally been achieved either by use of chiral catalyst 5 or by chiral dienophile. 6 In addition to the reports for the synthesis of chiral dienes, [7][8][9][10] their application in such reactions is noticed rarely primarily due to their difficult synthesis or low yields. Synthesis of glycosyl dienes and their applications in many cycloaddition reactions for the synthesis of a variety of compounds have received much attention recently.…”

exo-Glycal Chemistry: General Aspects and Synthetic Applications for Biochemical Use

“…Despite the wellknown use of this method for the generation of a double bond, the application to make C-glycoylidenes was not available until late 1990s. Both Taylor's and Franck's group reported almost at the same time the two-step route starting from S-glycosides, which included oxidation to give sulfone glycosides and elimination/arrangement to generate exoglycals, as shown in Scheme 8 [40,41]. In addition to achieving the preparation of di-, tri-and tetra-substituted exo-glycals, the former group carried out several synthetic applications of exo-glycals to produce C-glycosides, Cdisaccharides, spirocyclic sugars and C-glycosyl amino acids [42,43].…”