Glycoluril dimers 4a and 4b were prepared and successfully transformed to glycoluril dimeric clips 7a and 7b. 1H NMR spectroscopy was used to reveal that the dimeric clip 7b with methyl substituents in its structure exists as a mixture of two distinct conformers in D2O at ambient temperature, while 7a possesses only one stable conformer under the same conditions due to its bulky phenyl substituents. The coalescence temperatures for 7b and its precursor 5b were determined. Both dimeric clips 7a and 7b formed complexes with methylviologen in D2O in which each of two clip-binding sites was occupied by one molecule of the guest. Thus, this study uncovers possible use of glycoluril dimers 4a and 4b as general building blocks for glycoluril-based supramolecular host molecules with two binding sites in their structure.
