The highly stereoselective synthesis of 1,1'-disaccharides was achieved by using 1,2-dihydroxyglycosyl acceptors and glycosyl donors in the presence of a tricyclic borinic acid catalyst. In this reaction, the complexation of the diols and the catalyst is crucial for the activation of glycosyl donors, as well as for the 1,2-cis-configuration of the products. The anomeric stereochemistry of the glycosyl donor depends on the employed glycosyl donor. Applications of the produced 1,1'disaccharides are also described.

A novel approach to chiral anti-α,β-diamino acid derivatives through tandem orthogonal organocatalysis has been developed. Chiral phosphoric acid catalysts control the chemo-, regio-, and stereoselective addition of hydroxylamines to alkylideneoxazolones, while a phosphine catalyst promotes the isomerization of Z- alkylideneoxazolones to the more reactive E- alkylideneoxazolones.

Regio-and stereoselective synthesis of 1,2-cisglycosides has been achieved by catalytic anomeric O-alkylation using organoboron compounds. Modulating steric and electronic factors of both catalysts and substrates enables activation of the axially oriented anomeric oxygens of glucose-derived dialkoxyborates. The mild reaction conditions allow broad functionalgroup tolerance. This approach can be applied to the efficient sequential synthesis of oligosaccharides.

The highly stereoselective synthesis of 1,1'-disaccharides was achieved by using 1,2-dihydroxyglycosyl acceptors and glycosyl donors in the presence of a tricyclic borinic acid catalyst. In this reaction, the complexation of the diols and the catalyst is crucial for the activation of glycosyl donors, as well as for the 1,2-cis-configuration of the products. The anomeric stereochemistry of the glycosyl donor depends on the employed glycosyl donor. Applications of the produced 1,1'disaccharides are also described.

We explored direct dehydrative coupling of tetrahydro-2H-pyran-2,3-diol or a 1,2-dihydroxy sugar with various alcohols using a range of arylboronic acids. Among the catalysts, 2-borono-4-trifluoromethylbenzoic acid efficiently promoted acetalization of tetrahydro-2H-pyran-2,3-diol. Ferroceniumboronic acid showed the best catalytic activity for glycosylation of the 1,2-dihydroxy sugar. The major products were 1,2-cis-α-D-glucopyranosides. INTRODUCTION Glycosylation is a key step for the synthesis of oligosaccharides and glycopeptides with a range of biological activities. 1 Although there have been many reports on the glycosidic bond-forming reaction, new efficient synthetic methods remain to be explored from the perspectives of atom-economy, sustainability, yield, and selectivity. In the conventional glycosylation, glycosyl donors with acyloxy, alkylthio, halogen, 2,2,2-trichloro-1-iminoethoxy, and pent-4-enyloxy groups at the anomeric position are required for coupling with a free hydroxy group of a glycosyl acceptor in the presence of an appropriate Brønsted acid or Lewis acid (Scheme 1a). 2 The activated glycosyl donors are generally not stable and need to be prepared and stored with care. Furthermore, glycosylation sometimes requires more than the stoichiometric amount of activator or additive and cooling or heating of the reaction mixture to attain a high yield and α/β-selectivity. To overcome these limitations, we planned to investigate catalytic dehydrative glycosylation of 1,2-dihydroxy sugars as inactivated glycosyl donors in the presence of arylboronic acids 3 as catalysts (Scheme 1b).