Cycloglycolurils: Hybrid Glycoluril-Cyclobenzil Macrocycles.

Two novel glycoluril macrocycles have been synthesized from cyclotetrabenzil and cyclotribenzoin precursors using solvent-free condensations with urea. The crystal structure of the cyclotetra( p -phenylene)glycoluril macrocycle shows a twisted ring conformation, while that of the cyclotri( m -phenylene)glycoluril hybrid exhibits a distinct tubular supramolecular packing. These structures establish a potentially broad new class of macrocycles with intriguing guest binding properties owing to their available N-H motifs.