Copper Reactivity Can be Tuned to Catalyse the Stereoselective Synthesis of 2-Deoxy Glycosides from Glycals

Abstract

<p><a></a>We demonstrate that tuning the reactivity of Cu by the choice of oxidation state and counterion leads to the activation of both “armed” and “disarmed” type glycals towards direct glycosylation leading to the a-stereoselective synthesis of deoxyglycosides in good to excellent yields. Mechanistic studies show that CuI is essential for effective catalysis and stereocontrol and that the reaction proceeds through dual activation of both the enol ether as well as the OH nucleophile.</p>

Stereoselective Synthesis of Iminosugar 2-Deoxy(thio)glycosides from Bicyclic Iminoglycal Carbamates Promoted by Cerium(IV) Ammonium Nitrate and Cooperative Brønsted Acid-Type Organocatalysis

“…Conventional deacetylation was conducted by addition of NaOMe (0.1 equiv/Ac mol) in MeOH at RT, followed by neutralization with solid CO 2 , evaporation of the solvent, and purification by column chromatography. The starting derivatives 3,4di-O-acetyl-5N,6O-(oxomethylidene)nojirimycin iminoglycal (1), 12 methyl 2,3,4-tri-O-acetyl-6-thio-α-D-glucopyranoside ( 6), 23 Fmoc-Ser-O t Bu ( 18), 24 methyl 2,3,4-tri-O-benzyl-α-D-glucopyranoside (19), 21 20), 18 and methyl 2,3,6-tri-O-benzoyl-α-D-galactopyranoside ( 22) 22 were prepared according to previously reported protocols. : C,61.56;H,9.30;N,2.87;S,13.15.…”

“…1,2-O-isopropylidene-5,6-O-(o-xylylene)-α-D-glucofuranose(20),18 and methyl 2,3,6-tri-O-benzoyl-α-D-galactopyranoside (22)22 were prepared according to previously reported protocols. To a solution of iminoglycal 1 (193 mg, 0.76 mmol) in MeOH (4 mL), NaOMe (1 M) (152 L, 0.152 mmol) was added and the reaction mixture was stirred for 20 min, neutralized with solid CO2 and concentrated under reduced pressure.…”