Synthesis of C-Glycosylic Compounds Using Three-Membered Cyclic Intermediates

Irina   P.   Smoliakova

doi:10.2174/1385272003376148

Abstract

Numerous methods for preparation of C-glycosylic compounds (Cglycosides) have been developed. One general approach to the synthesis of these important O-glycoside analogs is based on the use of three-membered cyclic intermediates. The review is focused on the application of glycal and exo-glycal derived epoxides and episulfonium and iodonium ions for preparation of Cglycosides. Reactions of glycal epoxides with organocuprates, Grignard and organolithium reagents, allylsilane, sodio malonate, and lithium alkynyl derivatives have been shown to be convenient for stereoselective synthesis of both α- and β-C-glycosides. The unprotected C(2)-hydroxyl group in the products can be removed in two steps providing an easy excess to 2-deoxy-C-glycosides. Electrophilic addition of arylsulfenyl chloride (ArSCl) to glycals has afforded 2- (arylthio)pyranosyl chlorides. Upon the treatment with a Lewis acid, the chlorides have been converted to episulfonium-like intermediates. Reactions of the latter species with silyl enol ethers, TMSCN, allylsilanes, vinyl ethers, and heteroaromatic compounds have opened a new synthetic route to 2- (arylthio)-β-C-glycosides having a variety of functional groups in the lateral chain. The 2-arylthio group in the products can be selectively removed using Raney Ni or n-Bu3SnH/AIBN. Episulfonium ions generated from ArSCl adducts of 1-methylene sugars have reacted with O- and C-nucleophiles to afford Oketopyranosides and 1,1-dialkyl C-glycosides, respectively. Acid catalyzed and nucleophilic ring openings of spiro epoxides obtained from exo-glycals have occurred with opposite stereoselectivity. Iodoniumpromoted reactions of exo-glycals have led to O-ketopyranoside derivatives.

« Previous Next »