Self-assembled pentamers and hexamers linked through quadruple-hydrogen-bonded 2-ureido-4 [1H]-pyrimidinones

The preorganization of bifunctional 2-ureido-4-pyrimidinones mediated by either 1,3-substituted adamantane or meta-substituted phenylene ring linkers leads to the preferred formation of stable pentameric (1)5 and hexameric (2)6 assemblies, respectively. Despite the high binding constant of the 2-ureido-4-pyrimidinone dimers and the highly preorganized structure of the monomer, the predominant formation of cycles (1)5 and (2)6 in solution occurs only within a specific concentration range.