Stereoselective synthesis of 2-C-methylene glycosides and disaccharides via direct allylic substitution of hydroxy group in benzylated glycals |
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Authors: | Paramathevar Nagaraj |
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Institution: | Department of Chemistry, Indian Institute of Technology—Delhi, Hauz Khas, New Delhi 110016, India |
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Abstract: | InCl3 efficiently catalyzes allylic substitution of the hydroxy group of 2-C-hydroxymethyl glycals to afford a diversity of 2-C-methylene alkyl and aryl glycosides as well as disaccharides in high yields. This protocol surpasses the existing methods for the synthesis of 2-C-methylene glycosides as it obviates the need for functionalizing the allylic hydroxy group of glycals. The interest of this methodology relies on the extremely mild conditions required even with a free hydroxyl group at the allylic position of the glycals and that too only with a catalytic amount of InCl3. The reaction is fast (30 min.), stereoselective and is compatible with a variety of oxygenated nucleophiles including those possessing acid-labile groups. A mechanistic investigation on the direct formation of an α,α-(1→1)linked disaccharide derivative from 2-C-hydroxymethyl galactal reveals that the reaction proceeds through a domino Ferrier rearrangement followed by a facile 1,3-alkoxy migration. |
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Keywords: | Indium(III) chloride Stereoselective synthesis Glycosides Ferrier rearrangement Carbohydrates |
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