Formation of oligomeric and macrocyclic ureas based on 2,6-diaminopyridine.
The conversion of 1,3-bis-(6-amino-pyridin-2-yl)-urea (1) with N,N'-carbonyldiimidazole at high temperatures in DMSO yielded a mixture of defined cyclic trimers and tetramers. On the basis of model reactions, exchange reactions were evidenced, which convert the cyclic tetramer into a stable cyclic trimer. Linear even numbered oligomers were obtained in acetone under reflux where side reactions were suppressed. The pronounced tendency of cyclization is attributed to a preferred folded conformation of the urea bond between two pyridyl units.
Leibniz Institute of Polymer Research Dresden  e.V. Hohe Straße 6, 01069 Dresden, Germany.
Andrea
A
Gube
Hartmut
H
Komber
Karin
K
Sahre
Peter
P
Friedel
Brigitte
B
Voit
Frank
F
Böhme