The condensation reactions of the structurally similar monomers 1,3-phenylenediamine ( 1a ) and 2,6-diaminopyridine ( 1b ) with N,N -carbonyldiimidazole have been compared. Whereas the reaction of 1a resulted in an amino terminated oligomeric polyurea, a mixture of two macrocyclic trimers and one macrocyclic tetramer was obtained in the case of 1b . The three components of the mixture could be isolated by extraction with DMSO at different temperatures. The structure of the macrocyclic compounds was investigated by means of NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy.
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Böhme et al. (2002) studied this question.
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