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Herein we present the synthesis and evaluation of anion-binding properties of 12 new receptors from the unclosed cryptand family. Their core is built on the stable 26-membered tetraamidic macrocyclic scaffold, whereas various alkyl and aryl urea substituents were introduced after a yield-limiting macrocyclization step (65–98%). The receptors strongly bind anions, in particular carboxylates, even in a highly competitive solvent mixture (DMSO-d6+ H2O 95:5 v/v).

A new protocol for PTC-mediated O-alkylation of the intraannular position of 20-membered unclosed cryptands (UCs) is reported. In contrast to the classical, “direct” strategy, which requires functionalization of the lariat arm at the beginning of synthesis, this “indirect” approach enables the late-stage introduction of various benzylic substituents after an unfavorable macrocyclization step (11 examples, yields up to 98%). Notably, this method permits preparation of, previously inaccessible, crowded UCs bearing 1-acetylpyrene substituent and dimer joined by p-xylene linker.