Preorganizing Linear (Self-Complementary) Quadruple Hydrogen-Bonding Arrays Using Intramolecular Hydrogen Bonding as the Sole Force

In this article we describe a rational approach for prefixing multiple cooperative binding sites in an ideal spatial arrangement on a structurally rigid backbone, constrained <i>exclusively</i> by intramolecular hydrogen bonding. The idea is exemplified by the ability of the self-assembling constructs <b>1a</b>−<b>e</b> and<b> 2a</b>,<b>b </b>to form hydrogen-bonded dimers, whose structural preorganization has been solely effected by intramolecular hydrogen bonding. The readily accessible amidinourea backbone has been used as a common platform for the construction of a variety of such self-assembling systems. ESI mass spectrometry and single-crystal X-ray diffraction studies have been particularly effective in investigating the self-assembling propensities of these systems. Remarkably, most the H-bonded dimers reported herein undergo an unusual mode of self-assembly, using intermolecular four-membered ring hydrogen-bonded interaction, affording extended supramolecular networks.