A Facile Synthesis of C2-Symmetric Macrocyclic Polyethers by Photodimerization of Covalently-linked Flavonoid Derivatives

C-2-Symmetric cyclic polyethers were conveniently provided by the photochemical dimerization of covalently-linked 2-chromonecarboxylic esters. Irradiation of polyethers possessing 2-chromonecarboxylate groups at both ends efficiently promoted intramolecular [2+2] cyclobutane formation leading to 14- to 23-membered cyclic polyethers in good chemical yields and quantum efficiencies. X-ray crystallographic analysis revealed that the stereochemistry of the cyclobutane was the C-2-symmetric structure.