Beilstein J. Org. Chem.2013,9, 2336–2343, doi:10.3762/bjoc.9.268
ligands exerted high polymerization activity in the ethylene homopolymerization and copolymerization of ethylene with polar monomers.
Keywords: amidineformation; diimine; flow chemistry; polymerization; Introduction
The design of a ligand is a key step in the development of new catalysts because the
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Graphical Abstract
Figure 1:
Sterically crowded, and neutral chelating diimine ligands.
Beilstein J. Org. Chem.2012,8, 1652–1656, doi:10.3762/bjoc.8.189
reactions are described as an excellent synthetic tool for the synthesis of sterically highly hindered endothiopeptides. S-Methylation and subsequent amidineformation can be carried out in an inter- as well as in an intramolecular fashion. The intramolecular approach allows the synthesis of the bottromycin
this approach failed (as did all other activations investigated) because of the formation of thiazolone side product, which could not be cyclized.
In parallel, we tried to figure out if the amidineformation is possible with sterically hindered endothiopeptides (Scheme 2). As a model substrate we chose
obtained from endothiopeptide 2. Here, the expected amidine was only formed in a trace amount, and a range of side products was obtained.
Therefore, we decided to change our strategy and to replace the intermolecular amidineformation by an intramolecular one. In this case the peptide ring should be formed