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.