Cyclobenzoin Macrocycles: Guest Capture and Applications in Energy Technologies

Cyclobenzoins are organic macrocycles prepared by the benzoin condensation of aromatic dialdehydes. These compounds are easily derivatized into close to a dozen other macrocycle classes, which offer various supramolecular handles for the binding of environmentally and energy-relevant species in the solution and the solid state. Tetrameric cyclotetrabenzoins and their esters have been shown to bind CO₂ and other linear guests in their square-shaped central cavity, allowing their separation from competing species of different geometry. Cone-shaped cyclotribenzoin esters engage inorganic anions through convergent [C-H···anion] interactions. Oxidized cyclotetrabenzoin-cyclotetrabenzil-is both a useful component of organic Li-ion battery architectures and a versatile synthetic precursor to other macrocycle classes through various ketone/NH₂ condensation reaction. Hydrazones prepared by condensing cyclotetrabenzil with arylhydrazines have been shown to bind iodine from a variety of environments with capacities up to 4.15 g g^-1. Cyclotetrabenzil oximes have been studied in separations of C₂ and C₃ hydrocarbons, showing marked preferences for alkynes. New azaacene, cycloglycoluril, and azolophane derivatives prepared from cyclobenzils have been examined as optoelectronic materials, precursors to cucurbituril extended frameworks, and model systems for the studies of global aromaticity, respectively. This Minireview will summarize the cyclobenzoin research during the past decade and offer insights into possible future directions.