“SWEET” SUCROSE MACROCYCLES VIA A “CLICK CHEMISTRY” ROUTE - Click Chemistry in Glycoscience: New Developments and Strategies - page 228

“SWEET” SUCROSE MACROCYCLES
VIA A “CLICK CHEMISTRY” ROUTE

MYKHAYLO A. POTOPNYK AND SŁAWOMIR JAROSZ

9.1 INTRODUCTION

The term “click chemistry” was introduced by Sharpless in 2001 to describe the
processes which allow the connection of two molecules (or fragments) in a pre-
dictable way, providing well-defined products in high yields. These reactions should
be characterized by high atom economy, application of readily available reagents (or
their convenient precursors), be easy to perform, and should be rather insensitive to
environmental factors such as oxygen and water. All these parameters would allow
the connection of complex molecules through a relatively simple linker [1]. The 1,3-
dipolar cycloaddition of azides 1 and acetylenes 2 , known as Huisgen reaction [2, 3]
(Fig. 9.1), is one of the most convenient processes for the preparation of 5-membered
heterocyclic compounds. This process is easy to perform, has high atom economy,
and—moreover—the starting materials (azide and acetylene) are usually rather easy
to prepare. However, because it gives more than one product (1,4- and 1,5-adduct;
the ratio of them depends on the nature of the substituents R' and R”), it does not
fulfill all the requirements of the “click chemistry” philosophy.
In 2002, Sharpless introduced a small modification to this process relying on an
application of Cu(I) species as catalyst which resulted in the formation of the 1,4-
adduct exclusively [4]. At the same time, a paper by Meldal [5] describing the same
phenomenon appeared.
The Cu(I) species are provided either directly (as Cu(I), CuOAc, etc.) or generated
in situ (from CuSO 4 and sodium ascorbate) [6, 7]. More complex species such as