Synthesis of C-aryl-Δ2,3-glycopyranosides via uncatalyzed addition of triarylindium reagents to glycals

2,3-Unsaturated-C-aryl glycopyranosides are important intermediates in the synthesis of medicinally important C-aryl glycosides. Treatment of glycal acetates with triarylindiums in ether at room temperature gives good yields of C-aryl-Δ2,3-glycosides of predominantly α-configuration. The mechanism of this reaction likely involves the formation of an oxocarbenium ion intermediate via indium(III) Lewis acid-assisted ionization of the glycal C.3 acetate. Coupling of trivinyl- and tris(alkynyl)indiums with glycals similarly led to C-vinyl- and C-alkynyl-Δ2,3-glycosides in good yield.