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NIS. After 3 h at room temperature (to allow disaccharide 9 to
form) excess NIS and TMSOTf were added to activate 2b.
Product 15 was isolated in 44% yield following purification
on silica.
These experiments demonstrate the applicability of a mild
promoter such as 1 for room temperature one-pot reactions
where the reactivity of the building blocks can be tuned
accordingly by choosing the right combination of protecting
groups. It is important to note that although yields for the
one-pot reactions are moderate, they correspond to the
formation of two glycosidic bonds with no purification by
column chromatography in between steps.
In conclusion, we have shown the versatility of IL 1 in
combination with NIS to selectively promote at room
temperature activated glycosyl donors in presence of less
active glycosides. We have exemplified the usefulness of IL 1
in regio- and chemo-selective glycosylation reactions where
both donor and acceptor bear a free OH of distinct reactivity.
Furthermore, we have demonstrated that a mild promoter
such as 1 can be used for room temperature reactivity-based
one-pot reactions, whereby the building block reactivity is
tuned by the choice of protecting groups. To the best of our
knowledge, we have presented the first example of a one-pot
glycosylation reaction where a partially protected ‘armed’
monosaccharide glycoside is used firstly as the glycosyl donor
and the resulting product becomes the glycosyl acceptor in the
following step, without any protecting group manipulations,
in both a sequential synthetic approach and where all the
components are mixed together in one vessel at the beginning
of the synthesis. The recyclability properties of the IL
promoter are also very attractive in terms of green chemistry
and this combined with the ability of 1 to promote glycosyl-
ation reactions at room temperature makes this strategy
convenient and cost effective for automated oligosaccharide
synthetic protocols where no strict control of low temperatures
will be required.
We gratefully acknowledge financial support from EPSRC,
The Royal Society and BBSRC DTA and we thank
Dr Gregory M. Watt for fruitful discussions.
18 K. N. Jayaprakash, S. R. Chaudhuri, C. Murty and B. Fraser-
Reid, J. Org. Chem., 2007, 72, 5534–5545.
ꢀc
This journal is The Royal Society of Chemistry 2010
2108 | Chem. Commun., 2010, 46, 2106–2108