Differential O-3/O-4 selectivity in the glycosylation of N-dimethylmaleoyl-protected hexosamine acceptors: effect of a conformationally armed (superarmed) glycosyl donor

Silylated Sugars – Synthesis and Properties

Silicon has been used in carbohydrate chemistry for half a century, but mostly as a protective group for sugar alcohols. Recently, the use of silicon has expanded to functionalization via C–H activation, conformational arming of glycosyl donors, and conformational alteration of carbohydrates. Silicon has proven useful as more than a protective group and during the last one and a half decades we have demonstrated how it influences both the reactivity of glycosyl donors and stereochemical outcome of glycosylations. Silicon can also be attached directly to the sugar C-backbone, which has even more pronounced effects on the chemistry and properties of the molecules. In this Account, we will give a tour through our work involving silicon and carbohydrates.

1 Introduction

2 Conformational Arming of Glycosyl Donors with Silyl Groups

3 Silyl Protective Groups for Tethering Glycosyl Donors

4. Si–C Glycosides via C–H Activation

4.1 C–H Activation and Oxidation of Methyl 6-Deoxy-l-glycosides

4.2 Synthesis of All Eight 6-Deoxy-l-sugars

4.3 Synthesis of All Eight l-Sugars by C–H Activation

4.4 Modification of the Oxasilolane Ring

5 C–Si in Glycosyl Donors – Activating or Not?

6 Si–C-Substituted Pyranosides

7 Perspective

Acceptor reactivity in glycosylation reactions

The effect of the reactivity of the glycosyl acceptor on the outcome of glycosylation reactions is reviewed.

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

Silyl groups such as TBDPS, TBDMS, TIPS or TMS are well-known and widely used alcohol protective groups in organic chemistry. Cyclic silylene protective groups are also becoming increasingly popular. In carbohydrate chemistry silyl protective groups have frequently been used primarily as an orthogonal protective group to the more commonly used acyl and benzyl protective groups. However, silyl protective groups have significantly different electronic and steric requirements than acyl and alkyl protective groups, which particularly becomes important when two or more neighboring alcohols are silyl protected. Within the last decade polysilylated glycosyl donors have been found to have unusual properties such as high (or low) reactivity or high stereoselectivity. This mini review will summarize these findings.