Catalytic Approaches to Chemo- and Site-Selective Transformation of Carbohydrates

Carbohydrates are a fundamental unit playing pivotal roles in all the biological processes. It is thus essential to develop methods for synthesizing, functionalizing, and manipulating carbohydrates for further understanding of their functions and the creation of sugar-based functional materials. It is, however, not trivial to develop such methods, since carbohydrates are densely decorated with polar and similarly reactive hydroxy groups in a stereodefined manner. New approaches to chemo- and site-selective transformations of carbohydrates are, therefore, of great significance for revolutionizing sugar chemistry to enable easier access to sugars of interest. This review begins with a brief overview of the innate reactivity of hydroxy groups of carbohydrates. It is followed by discussions about catalytic approaches to enhance, override, or be orthogonal to the innate reactivity for the transformation of carbohydrates. This review avoids making a list of chemo- and site-selective reactions, but rather focuses on summarizing the concept behind each reported transformation. The literature references were sorted into sections based on the underlying ideas of the catalytic approaches, which we hope will help readers have a better sense of the current state of chemistry and develop innovative ideas for the field.

Direct synthesis of C-glycosides from unprotected 2-N-acyl-aldohexoses via aldol condensation–oxa-Michael reactions with unactivated ketones

C-glycosides were synthesized from unprotected 2-N-acyl-aldohexoses and unactivated ketones in one pot via aldol condensation–oxa-Michael reactions.

Multicomponent Cascade Reactions of Unprotected Ketoses and Amino Acids--Access to a Defined Configured Quaternary Stereogenic Center

A highly stereoselective multicomponent cascade reaction of ketones with unprotected amino acids was developed. This operationally simple methodology was expanded to reactions of unprotected ketohexoses and unprotected amino acids. By the careful choice of amino acid and isonitrile, an optional access to all possible enantiomers is given.

The long underestimated carbonyl function of carbohydrates – an organocatalyzed shot into carbohydrate chemistry

Several novel and highly stereoselective C–C bond formation processes of unprotected carbohydrates are described.

Amine-catalyzed cascade reactions of ketoses with 1,3-dicarbonyl compounds

An amine-catalyzed cascade reaction of ketoses with 1,3-dicarbonyl compounds is described.