ABSTRACT
An efficient and practical approach for the synthesis of 3-indolyl-C-Δ1,2-glycosides through a palladium-catalyzed annulation/C-glycosylation sequence of o-alkynylanilines with 1-iodoglycals has been developed. This methodology has a wide scope of substrates and gives access to 3-indolyl-C-Δ1,2-glycosides in high yields. Furthermore, the product obtained here exhibits a high utility for further transformations.
ABSTRACT
The total synthesis of rebaudioside S, a minor steviol glycoside from the leaves of Stevia rebaudiana, was investigated via a modular strategy, culminating not only in the first and highly efficient synthesis of Reb-S and analogues thereof but also in the revision of the originally proposed structure. The modular strategy dictated the application of C2-branched disaccharide Yu donors to forge C-13 steviol glycosidic linkages, posing considerable challenges in stereoselectivity control. Through systematic investigations, the effect of the internal glycosidic linkage configuration on the glycosylation stereoselectivity of 1,2-linked disaccharide donors was disclosed, and the intensified solvent effect by the 4,6-O-benzylidene protecting group was also observed with glucosyl donors. Through the orchestrated application of these favorable effects, the stereoselectivity problems were exquisitely tackled.
