Total Synthesis of the Purported Structure of Branched Resin Glycosides Merremoside G and H 2 .

The first total synthesis of the purported structure of branched resin glycosides merremoside G and H 2 is accomplished. A signature step is represented by the sequential transition-metal-catalyzed coupling of stable trisaccharide homoallylic alcohol and monosaccharide alkoxyallene to afford the pentasaccharide skeleton. This de novo strategy is conducted under mild conditions with no need of preactivation. In addition, it allows for efficient preparation of the target compounds in combination with late-stage functionalization.