Silylated Sugars – Synthesis and Properties

Abstract

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 Introduction2 Conformational Arming of Glycosyl Donors with Silyl Groups3 Silyl Protective Groups for Tethering Glycosyl Donors4. Si–C Glycosides via C–H Activation4.1 C–H Activation and Oxidation of Methyl 6-Deoxy-l-glycosides4.2 Synthesis of All Eight 6-Deoxy-l-sugars4.3 Synthesis of All Eight l-Sugars by C–H Activation4.4 Modification of the Oxasilolane Ring5 C–Si in Glycosyl Donors – Activating or Not?6 Si–C-Substituted Pyranosides7 Perspective

Approach Toward Reversal of Chemoselectivity in Catalytic Silylation of Pyranosides

“…Site‐selective functionalization of carbohydrates with multiple hydroxy groups attracts much interest in synthetic organic chemistry, [1] because it enables late‐stage functionalization of sugar‐related bioactive molecules [2] . While silylation is one of the most frequently used methods for the protection of simple alcohols and complex polyols including carbohydrates, [3,4] studies on site‐selective silylation of sugar derivatives under catalyst‐controlled conditions have been rather limited [5] . Shalf and co‐workers reported transition metal‐catalyzed site‐selective disilylation of unprotected pyranosides with trialkylsilanes as silylating agents, where the inherently most reactive primary C(6)−OH and the secondary C(3)−OH of a glucopyranoside undergo selective silylation [5a,b] .…”