Novel Platinum-Catalyzed Ring-Opening of 1,2-Cyclopropanated Sugars with Alcohols: Stereoselective Synthesis of 2-C-Branched Glycosides

Reaction of 1,2-cyclopropanated sugars with a catalytic amount ofZeise's dimer [Pt(C2H4)Cl2]2 and an alcohol gives 2-C-branched glycosides by a novel platinum catalyzed ring-opening. A wide variety of alcohols can participate in this ring-opening reaction giving 2-C-branched glycosides ranging from methyl glycosides to complex disaccharides (17 examples). Very high diastereoselectivity is obtained at the newly formed C-1 stereocenter strongly favoring the alfa-glycoside. The mechanism presumably involves the formation of an intermediate platinacyclobutane which undergoes ring-opening at C-1 by the alcohol followed by reductive elimination of platinum.