Synlett 2009(7): 1154-1156  
DOI: 10.1055/s-0028-1088105
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of 2,3-Unsaturated O- and N-Glycosides by HBF4˙SiO2-Catalyzed Ferrier Rearrangement of d-Glycals

Oscar Mariano Rodríguez, Pedro Alfonso Colinas*, Rodolfo Daniel Bravo
LADECOR, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 y 115 (1900) La Plata, Argentina
Fax: +54(221)4226947; e-Mail: pcolinas@quimica.unlp.edu.ar;
Further Information

Publication History

Received 1 January 2009
Publication Date:
20 March 2009 (online)

Abstract

Fluoroboronic acid adsorbed on silica gel (HBF4˙SiO2) catalyzes the Ferrier rearrangement of per-O-acetylated glycals with alcohols and sulfonamides to give 2,3-unsaturated O- and N-glycosides in good to excellent yield and with high α-stereoselectivity.

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Experimental Procedure
To a solution of the glycal (0.5 mmol) and the nucleophile (2 equiv) in dry MeCN (4 mL), the catalyst was added at 40 ˚C. After stirring for the time indicated, the reaction was filtered and the solvent evaporated in vacuo. The residue was chromatographed on SiO2 (eluent hexane-EtOAc) to afford the glycosides.
Preparation of HBF 4 ˙SiO 2
A magnetically stirred suspension of SiO2 (13.4 g, 230-400 mesh) in Et2O (37 mL) was treated with 40% aq HBF4 (1.5 g) for 3 h. The mixture was concentrated and the residue dried under vacuum at 100 ˚C for 24 h to afford HBF4˙SiO2 (0.5 mmol g). [³0]

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The ¹H NMR (200 MHz) spectra of the glycosides confirmed the α-configuration of the products formed in the reactions by comparison with the literature data.